From what I can see in the error message, the issue is related to modifying a collection while it is being enumerated -- an operation that is not allowed in C#. This error is coming from the Asset Database. The culprit is 1) the Move It mod (because it deals with asset repositioning which can trigger database changes), as Andrew stated. 2) A different mod that manages assets/prefabs (because it modifies resources from the Asset Database mid-operation), or 3) a UI mod that adjusts game settings therefore interacting with the database.
If you do not have the Move It mod, I suggest you first disable all mods -- load the game to make sure you do not flag (trigger) the error. Then, turn each of your mods on one by one to see if one of them flags the error.