Eleeist

Steps to reproduce:
Select post in topic with a checkbox for multimoderation With post selected, click the ellipsis and delete this post from there The multimoderation action bar on the bottom of the page still shows that there is one post selected

So taking a look at this, Im unable to find any common thing between your sites, and unfortunately Im unable to replicate the issue in any way. Of course, its obviously happening, but doesnt really change the fact we cant replicate to see the issue in action. If any of you manage to find a way to replicate and can give me step by step how to do so, please let me know and I can then get this resolved.

I, too, have seen this on my website occasionally. Members displayed and logged in anonymously. I chose not to seek support for it due to the harsh frustration you, the IPS support, put its self-hosting customers through when I reported issues with your software. You always try to blame every issue I have on my hosting provider or third-party resources. 
Yes, this issue of anonymous login by non-anonymous members is real. 

Search engines look for the Title and Description first, not URL. There are meta tags that are important. As for now all your categories have the same title and no description.
You have to go to System -> Site Promotion -> Search Engine Optimization and then provide for each URL the title and description that includes the car model. Example:

I would not mess with URL structure. The URL is almost unimportant if your page title and description are set properly. 😉 Tip: if you use the category description field in forum, it will be automatically mapped into a meta description tag.

This is the same.
Open forumRow template bit, find:
Find:
{{$count = \IPS\forums\Topic::contentCount( $forum, TRUE );}} Change to:
{{$count = (int) \IPS\forums\Topic::contentCount( $forum, TRUE );}}  
Does it help?

Since applying the 4.7.16 hotfix from today, on default theme with no modifications, we started getting template error in forums.front.index.forumRow template in one of the forums.
On further debugging
{{$count = \IPS\forums\Topic::contentCount( $forum, TRUE );}} returns post count followed by plus sign +, which throws when passed to
{number="$count" format="short"}  since it's not a number.
This happens for just one subforum.
I've updated site access details in Client Area if you would like to have a look 🙂 The forum ID which returns this strange count is 111.

Since applying the 4.7.16 hotfix from today, on default theme with no modifications, we started getting template error in forums.front.index.forumRow template in one of the forums.
On further debugging
{{$count = \IPS\forums\Topic::contentCount( $forum, TRUE );}} returns post count followed by plus sign +, which throws when passed to
{number="$count" format="short"}  since it's not a number.
This happens for just one subforum.
I've updated site access details in Client Area if you would like to have a look 🙂 The forum ID which returns this strange count is 111.

Since the upgrade to 4.7 we have lost the ability to see anonymous users in Recently browsing list. Before upgrade (4.5), we could see them in the list marked with crossed eye like this:

After the upgrade, we cannot see anonymous logged users at all. I am logged in as administrator (anonymous login required). My moderators are logged as anonymous if they like. The most of them like. 😉 Now, I can see myself on the list without crossed eye and non-anonymous users. My moderators cannot see me. I cannot see my moderators.
We have used this feature to see if there is a moderator online in the “critical” topics that are going to escalate. 
Has the feature been removed? Or are there any settings that I miss? 

We released Beta 5 a short time ago to address this issue.

Same thing happens for me in ACP when editing templates etc.
The codemirror.js is missing semicolons in few places, had to patch it up to edit my theme.

Well, I jumped the gun here - indeed after the conversion completed the background processes kicked in, so I guess this answers it. Thanks! 🙂

Have all background tasks completed in ACP > System > Dashboard? The BBcode would be done in a build process post conversion.