Okay, so: I tested it with the weather machine: make sure you have enough upgrade parts, have a level 10 handiness skill, and upgrade the weather machine fully. Then test it out with your mods: make it winter for a while, then make it spring, and see if the snow melts or not.
I tested it everytime adding 3 extra mods (depending on how many mods you have, this might take a while...) I had no issues, so it's probably one of these 3 mods I deleted before I started to test out what the issue was, bacause I didn't want them anymore or I thought were sus because they were a bit old. The mods I deleted were: Roarsome Kids Bedroom, Rustic Romance, and the ParenthoodBunk. If you have the same issue and have any of these mods installed, delete them and the issue might be resolved.