when i have the slow falling effect and i go to crit a player/ entity the crit particles display on my screen but there is no crit noise and no extra damage being dealt. this is especially concerning in pvp scenarios as slow falling is a powerful debuff that can remove a players ability to crit.
there is also a RANDOM chance of the crit actually working however, i think for a balanced pvp experience crits should be possible at all times when falling, even with slow falling effect.

how to reproduce, simply give yourself slow falling and try to jump and hit something while falling down,  theres about a 95% chance that you wont be able to crit.