It is probably something on your end. I have no issues joining modded servers and even have my own. Try unsubscribing from all mods and re-downloading them, there might be some corruption. If this doesn’t solve the issue, then arrange your mod order to match the one required by the server from the launcher.
Been there done that. Someone suggested that it was steam family sharing that is interfering but I backed out of that long time ago and deselected the family sharing option.
Unsubscribe from the mods, delete what is left in the content folder \steamapps\workshop\content\440900
and then verify the integrity of the game files.
A big portion of the people on PC are playing on modded servers. If it was an issue for the last 6 months, we would know by now. It is definitely not a common issue. It is also normal for the game to restart after a mod mismatch. It is to arrange the mods in the order required by the server you are attempting to join.