I recently made my first winter custom multiplayer map but the game doesn't select winter skins ingame.
https://www.coh2.org/topic/11228/how-to-winter-skins-in-custom-maps
I would start by opening the .OPTIONS file in notepad and verifying USES_ICE in there.
Other than that, I would just assume Relic broke it at this point
EDIT:
If your base buildings are correct then USES_ICE is working. I think this also sets the vehicle skins to winter.
If the soldiers are not using winter, the INFO text has an issue. Was it saved with the wrong SUFFIX? Notepad likes to add a .TXT to the end so you may have edited it correct but not saved it correct and are still using the old file?