@magge The OP sounds like it's an issue joining games in the first place, whereas those errors would be things that occur during an actual game (that has started). I've not heard of M27 causing any issues with joining games so think it's unlikely, although one thing to try to make sure @zorg-kirill would be to disable all sim and ui mods and see if you still get the crash (and if not then enable them one by one).
In terms of the error/warning messages highlighted unfortunately M27 will generate a lot of warnings and errors in the logs. For example the one about no valid units is something that happens regularly that I've not got around to properly investigating (I'm fairly confident it's a false error the vast majority of the time, but figuring out how it arises and how to not have it show the message when it's not an issue without slowing things down is harder). They're also things that would affect how M27 plays in the game (rather than something that would cause a crash).
If the game is crashing (i.e. during the game) with M27 enabled though I can look into further as that's something I've seen happen before