Kind of nitpicky since 99% will never rollback to a previous version of Unturned but yeah.
Rolling back Unturned to a previous version (anything before 22.214.171.124) will result in a blue screen of death upon launching the game. Stopcode is Worker_Invalid. This will occur even on fresh installs of Unturned. Have tested it on 3 different machines, all of which can run the up-to-date version of unturned without issues.
Again, really tiny issue due to the fact that most people will not use it, but yeah.
EDIT: Just for extra info, this also happens when launching the game without BattleEye being enabled.