the map shown in the video is christmas_in_the_suburbs, so i'll assume you meant that. if it's only happening for you, only thing i can think of rn would be
clearing other folders from your gmod folder (common\GarrysMod\garrysmod) like the cache, data, and download folders. feel free to make backups too.
turning off steam cloud sync for the next time you install gmod (you'll have to redo binds)
clearing addons
and make sure you don't have 2 gmod installs.