The number of times I've gotten two or even three critical failures/misses in a row is mind boggling. That said I've watched the NPCs do it as well, so there is a semblance of fairness. You're right that the statistics feel off, but as is always the case, our minds are going to focus on these outliers without recalling all the many times the dice fell right in line with expectations.
I do swear that a 50% chance to hit with a Sacred Flame consistently feels more like a 15% chance.