Makoto

If you search for Email Error Log in your AdminCP, do you see any recent errors log entries for @me.com addressees?

No, the files that you download from Invision are the core software files. They only contain code, none of the files you are overwriting contain your own data. This information is either stored in the database, or as independent files in upload directories of your installation. Overwriting will never erase any content you have on your community.
However, I am concerned over the missing database error you are seeing, but I don't know just how far back you upgraded from. Just to be clear, if this table is missing and there is any data missing as a result, it won't be from overwriting the upgrade files as mentioned above, this is a problem that already exists.
But until you properly fully upgrade all your invision files and run the upgrade properly, we won't be able to confirm for sure if any data was lost.
But it's always a good idea to make a full backup if you can before upgrading regardless, including of your database.
Additionally I have to ask, when you upgraded the core invision software or any other applications, did you skip replacing those files as well?

No, the files that you download from Invision are the core software files. They only contain code, none of the files you are overwriting contain your own data. This information is either stored in the database, or as independent files in upload directories of your installation. Overwriting will never erase any content you have on your community.
However, I am concerned over the missing database error you are seeing, but I don't know just how far back you upgraded from. Just to be clear, if this table is missing and there is any data missing as a result, it won't be from overwriting the upgrade files as mentioned above, this is a problem that already exists.
But until you properly fully upgrade all your invision files and run the upgrade properly, we won't be able to confirm for sure if any data was lost.
But it's always a good idea to make a full backup if you can before upgrading regardless, including of your database.
Additionally I have to ask, when you upgraded the core invision software or any other applications, did you skip replacing those files as well?

I have no idea why you would be missing database tables for the pages application without explicitly uninstalling it, the table you're showing as missing shouldn't be a new table or anything of the sort that I'm aware of.
IPS should not touch the table when upgrading other applications.
Are you able to access phpMyAdmin or any other database management utility on your server (including the MySQL command line if you're comfortable using it) and show us all database tables you have on your forum that have ccs_ in the table name?
What happened immediately prior to your forum going down entirely? Did you try and change or upgrade anything?

It might be that they are transferring the photos from their iphone to other devices in some other manner, and then trying to upload the images on non-iphone devices?
That could be what's happening instead of them uploading straight from their phone. It could also be that this auto conversion only happens in more modern versions of iOS. I have no idea honestly since I have no apple products.
But if multiple users on your forums are reporting it as an issue it could be worth having a plugin made for it.

You can download a copy of IPS and all your purchased applications from the client area here:
https://invisioncommunity.com/clientarea/
Click on the license you wish to use, and there will be a download button at the top of the page.
Extract this, and upload everything in the applications/cms folder to your live installation. It is safe to overwrite any existing files.
Once you do this, go into the AdminCP again and you should see an option to upgrade your pages installation.

It might be that they are transferring the photos from their iphone to other devices in some other manner, and then trying to upload the images on non-iphone devices?
That could be what's happening instead of them uploading straight from their phone. It could also be that this auto conversion only happens in more modern versions of iOS. I have no idea honestly since I have no apple products.
But if multiple users on your forums are reporting it as an issue it could be worth having a plugin made for it.

Looks like a potential compatability issue with this plugin,
 
Can you try disabling it and see if the error goes away?

@Alexander Yuganov When you're on the edit screen for your theme as shown in the original screenshot, add this at the end of the URL after the "&id=<your_theme_id>",
&t_type=css&t_app=core&t_location=global&t_group=framework&t_name=data-lists.css Then hit enter and you should have the data-lists.css file open in your editor. You can then just click the revert button, and it'll reset back to the default layout, or compare between the two files and see if there are any tweaks you may need to port over to your custom.css file.
I recommend making a backup in a local text editor before you revert, just in-case reverting breaks something in your custom template.
Also note you don't need to hit save after hitting revert, as doing this will just mark the CSS file as modified again.

Even CloudFlare appears to have zero support for it,
https://developers.cloudflare.com/images/faq/#can-cloudflare-images-use-the-heic-heif-format
Honestly not sure it's worth the hassle. Are you seeing these images posted a lot on your community, or just once in a blue moon?
If ImageMagick supports the format you could theoretically just have them converted to another format. I believe a plugin could accomplish this. But if it's not a common issue I wouldn't personally bother.

What does the error log say now?  You still have not shared what it's mentioning is the current problem.  
Also, have you checked to make sure your server meets the minimum requirements for this version of IPB?  
 

In that case, I might look at antivirus software or other firewall software running on the device that could be intercepting requests.   Heck even adblockers as it could be blocking the IPS JS. 

Wouldn’t worry too much about these unless you’re seeing a specific slow issue on your site really. We, of course, regularly review queries and update performance when reported in certain areas but bound, on need, to have queries meet these circumstances where they are joined with no index and/or use DISTINCT. These performance tools often assume you live in a vacuum which is unreasonable. 

Not at the moment, but it's a feature I can look into implementing in the next major update!

Please make sure your file permissions for all your IPS files are set up correctly too.
However, if you are running the latest version of IPS, then PHP 7 is indeed not supported anymore.
As for suggestions, we unfortunately can't provide you with hosting suggestions outside of CiC here.

No problem, just let me know if you run into any other issues!

🤦‍♂️
Sorted, thanks, I knew it would be something simple.

Have you set up any tags in the Customization page of the Radical Tags application yet?
You'll need to add some there, and then you can define which prefixes can be used in a specific forum if you need to.

The button comes from this resource:
And it removes the follow, not the content. 👍

Re-uploading the core files will only prompt you to update the applications you haven't already updated (in this case commerce)
It won't have any impact on the forums application, which has already been updated.
You could download the entire suite from the ACP and then upload upload the commerce/nexus application in the applications folder of that download, but I might suggest doing a full upload anyways just to make sure everything did get uploaded correctly when you did the initial upgrade.
IPS shouldn't let you upgrade if any of the files for a specific application weren't uploaded properly (so this means the forums, core software and other applications you updated should be fine), but it can't hurt to be extra sure.

It depends. You ideally don't want it so small you end up having to make a crazy number of requests for larger uploads. For a 1GB file, you'd need to make 100 requests to finish uploading a file, which is a decent bit, but as this isn't sustained traffic it's not the worst thing. People with faster connections may hit you with a large spike of requests when uploading larger files, as a gig line can push 10MB of data in no time at all, so just need to make sure you can handle that if you want to keep it at a lower value.
You could increase it a bit if you wanted to reduce that overhead a bit, as 10MB is pretty low. But unless you're noticing performance issues, particularly when uploading files, it's probably not a big concern.

Looks like this application may have some PHP compatability issues which are preventing your tasks from running properly,
Try disabling it and see if that resolves the issue. If it does, then you'll need to contact the author of this application and let them know of the errors.
 

Looks like this application may have some PHP compatability issues which are preventing your tasks from running properly,
Try disabling it and see if that resolves the issue. If it does, then you'll need to contact the author of this application and let them know of the errors.
 

Can you make sure you have these settings enabled under the Configuration option in the Radical Tags tab?

If they are already both enabled, can you check and see if the issue persists when you switch to the default/stock IPS theme?

Happy to hear it! If you run into any other issues just let me know.