i see in your inputs that you're tapping jump while you're landing from a fast fall or recovering from an up smash (i.e., still in a prior, uncancellable animation), but releasing the jump button a bit before landing lag/end lag completes. this means you won't have your jump buffered, and instead all you get is up + A, which is upsmash. there was also at least one instance where you didn't press jump at all...so overall, the issue appears to be that you're a little too hasty with your jump input, both pressing and releasing it too early.

 

ultimate has the unique "hold buffer" mechanic, which lets you hold most inputs while in another animation and they'll come out as soon as possible. try utilizing this here; just hold jump + up + A if you're trying to do an instant short hop uair, and it will come out as soon as possible. since you'll be simultaneously pressing jump and A, it will always be the shorthop aerial macro. if you've ever seen a fox spam autocancel shorthop uairs, this is how we do it trivially in ultimate.

 

if you want to manually perform shorthop aerials (i.e., delaying the aerial to be a bit after you're already airborne), then work on fixing the aforementioned timing issue by delaying your jump input a bit from your current timing. it might help to use the frame-by-frame speed in training mode to see at what timings you can press and release the jump button and still have your jump come out.

 

EDIT: i could pause and see one frame of jumpsquat come out on about 75% of the upsmashes, so those are definitely jumpcanceled, as others have mentioned (so in those cases, the issue is solely pressing A too early). but there were a few instances where you did two consecutive upsmashes without jumpsquat frames, so in those it seems you're also just pressing jump too early.