Running a dedicated server, I've localized my crashes to two mods: RR-MedievalRoleplayDeco! and Tek 2.0 (CrossPlatform), using either of these results in the crash. If I don't use either but do use a range of other mods and I can log into the game normally.
Simply not using the mod isn't a workable option as uninstalling them means losing everything built with them to say nothing of the game play they enable. Not something that can't be overcome, but a bitter pill to say the least. For now, I've shutdown the server and my players and I have given up on the game until those mods are usable again.