Lot of problems upgrading 3.4 to 4.1

[Retroforum]

I've tried, tried, tried, but everytime it fails: upgrading 3.4 to 4.1
I already tried to upgrade to 3.4.9 (which works but breaks some stuff) and then to 4.1.11, but it fails on an error that should have been solved since 4.0.13
Also the conversion to UTF8mb4 broke a lot of stuff

Here's the story:

1st part of the upgrade works fine, but then error after error:

After the 3rd error I can't continue.

The conversion to UTF8mb4 lead to questionmark Unicode characters, I can't fix them. I do have a backup of the old, unconverted database but I will miss a week of posts when I go back.

Please help, I'm stuck with 3.4.9 which also has an error: when I press 'submit' to a post it doesn't show that it's posted, but it is. When I post again it appears twice. 

[steve00]

Perhaps better to fill out support ticket in Client Area as not really able to help with what info you have given

[Retroforum]

Thanks, I don't know what more info I can give actually.

[opentype]

IPS support will be able to check it out on your site directly. That’s probably the only thing that might resolve it. 

You might also consider to go back to the last backup and then let IPS do the upgrade.