When you load in a character with LoadCharacter(), players will often load with duplicates (and even triplicates on repeat spawns) of all of their vanity items. This causes some serious weight issues for players with bigger hats, and it also just bulks up the Character model really badly. Certain objects like BodyColors are also cloned.
I tested this in two separate games of mine to make sure it was a global issue. Maybe it only affects when you’re testing solo in Studio, though.