Are hit percentages remotely accurate?

The chance of missing 4-5 75%+ chances should be extremely low. However, it happens multiple times per mission. Since I'm playing on Brutal difficulty, this often results in someone dying.

I've checked and nobody has the Optimistic trait. There is no indication the chances shouldn't be correct, though there may of course be something I'm missing.

I am aware RNG means random but this doesn't seem close to what it should be. Is there something reducing chances not reflected in the percentages? If so, what should I expect from an 80% attack?