So me and my friend recently started to work together and for the first time ever, ive encountered a bug with the StarterCharacter.
Ive done a lot of changes, even setting everything to collide, and changed collision box to Box.
Ive tried resizing and so on, however no matter what I do, whenever I walk without jumping, I walk right through parts. Mean while, when I just collision fixes itself magically. Yet, once you land and move around without jumping, you can walk through things.
From what I can see your issue is related to this thread.
As a quick fix you can either rename a part to Torso or disable RunningNoPhysics on spawn (i.e utilising the .CharactedAdded event. (check above thread).
Yeah, definitely not your fault – there are probably 100s of cases in the engine where humanoids rely on named parts, and only 2 of them are documented. As mentioned on the other thread, this is awful behavior, and every time you encounter one of these cases, you should file as a bug.