For supers, the two punch buttons can be pressed up to 3 frames apart and the super will still come out. I don't honestly know if pushblocks have the same kind of leniency.
They do, anything requiring PP or KK uses the same code path (pushblock, supers, unfly, dashing, etc). It's 2 frames, though, not 3.
AI did 3 s.HP hits, pushblock worked only on the last, though the first two weren't registered as PP. Not sure what's up with that, but I really don't recall this problem being the case like a year ago or so.
In the first two examples those buttons are pressed WAAAAAAY further apart than 2 frames. 4-6 frames at least.
The unfortunate answer to your question is PEBCAK (user error). In your video it's
really obvious.
Edit: I don't have a problem with PP supers.
Supers can be negative-edged, for example:
Press MP ... Press HP + Release MP
or
Press MP ... Press HP, Release HP + Release MP
will count for a super because you are negative-edging one or both of the buttons.
I really don't recall this problem being the case like a year ago or so.
Well then, either you got worse, or your hardware degraded.
According to version control, no code or script even remotely associated with input processing or pushblocking has changed in any way since...let's see...December 24th, 2013.
I've honestly had this problem too where i mash pushblock but get nothing. I thought i was just bad.
See the answers above.