ImNotRen fixed. The issue was Spanish extension after that extension update, complaining about illuminate/container too.
Reinstalling all composer packages fixed that. I'd suggest that we'd need to reinstall vendor on base forum and then sync it, which will take ± 2 hours.
Another thing is that the Mathren extension now should work again too. But all forums having Spanish extension will get the error, so if it's urgent, please report it. Thank you and sorry for the inconvenience.
Update: All forums are being synced now, which will take some time. When that is finished, everything should be alright. This was my first mass extension installation process, so I apologise for some troubles there and here.
