While doing an upgrade on my River's Huts mod i found a bug that crash the game. It is related to the number of different alternate models the templates have.
if we have an house with 3 alternate models (3 colors for example) and we put an upgrade button to a template that hold 6 different alternate models : NO PROBLEM
But if we have an house with 6 alternate models (6 colors for example) and we put an upgrade button to a template that contain only 3 different models : CRASH 50% of the time.
So the way to fix it, you need to add enough models (even if you just duplicate the existing ones) to equal or more than previous template (example from 6 models to 2X3 models =6 to prevent crash)
This is just an headups to how to fix a bug that crash game for that particuliar case.
Enjoy!