Hey,
I've been getting this error since the Airports DLC was released along with the CCPs. I've ignored it as the game has worked fine, however, just the other day my game suddenly gave me an error with an array issue and being out of range (sorry I forget what the exact error code was) and I now can't do anything. Looking online there's a chance it could be due to MOM but the error code that's preventing me from doing anything else has no context, just that there is an error with the array and something is out of range. I've added in the error I get for Building Themes. Any help would be greatly appreciated!

The Mod C:\Program Files (x86)\Steam\steamapps\workshop\content\255710\466158459 [BuildingThemes.dll] has caused an error [ModException]

Details:
System.NullReferenceException: Object reference not set to an instance of an object
at BuildingThemes.Debugger.AppendModList () <0x00199>
at BuildingThemes.Debugger.OnLevelLoaded () <0x0001c>
at BuildingThemes.LoadingExtension.OnLevelLoaded (ICities.LoadMode) <0x0003b>
at (wrapper dynamic-method) LoadingWrapper.LoadingWrapper.OnLevelLoaded_Patch4 (LoadingWrapper,SimulationManager/UpdateMode) <0x000b9>