I missed 6 time in a row with 81% hit chance. Nothing is impossible but here the probability is less than 10^-3.
This is a 1 in ~20.000 chance, not that hugely far off Tim Cain's Fallout example. It's long odds, but given the number of rolls and players, it should occur with some frequency.
The problem is that it happens consistently to the same player and across the player base. As for the fact that if you have a 3:1 critical miss/critical success ratio is indicative the RNG doesn't work properly.
Or rather, players are anecdotally relating their experience of this happening to them which is not necessarily the same thing as it actually happening. Unless we look at the numbers (the game engine numbers, not the statistical math based on the anecdotes) this is just a bunch of people going "I feel like...". Which is fine and can totally be relevant feedback but in terms of specific criticism of a random number generator "I feel like I miss a lot" isn't really too meaningful due to, amongst other things, Gambler's Fallacy and Confirmation Bias.
Sometimes I get really annoyed at my companions too because it feels like they mess up a lot but as a gut feeling from looking at the stats of NPCs and pretty solid knowledge of the D&D system, I'm fairly confident (but unable to provide solid evidence for) that the system is working as intended and that if anything needs tweaking it can probably be fixed by modifying enemy statistics rather than looking at the RNG.
