I'm not sure this is relevant for you, but when I grow impatient with people, I suspect it has more to do with my attitude towards myself. It stems, I think, from a tendency to be too hard on myself. To judge myself too harshly for making mistakes.
I used to not see any problem with this. I used to think it helped me do things better, helped me become a stronger individual. I also reasoned that, if a side-effect of this was that I was really hard on others, it was ok, because at least I was being fair. It's not as though I was holding anyone to a different standard than i held myself.
Recently, I've reevaluated my opinions. After much thought, I've come to the conclusion that this kind of behavior is good neither for myself, nor for others.
The reason it wasn't not good for myself was that I got really defensive. It made it hard for me to take criticism, even honest, reasonable criticism. I tended to react to criticism with scorn or distress. It wasn't easy for me to admit, in the moment, that I'd done something wrong. I would instead simply shove the blame onto someone else. Because I used to beat myself up over every mistake, it made me less willing to notice my mistakes.
This seemed to be some sort of emotional reaction. On occasions when I made a mistake, I would subject myself to a lot of distress. As a way of protecting myself from this, I think my brain became less receptive to acknowledging mistakes (regardless of who brought them to my attention).
The reason it wasn't good for others was because many people are very sensitive about the way in which they are criticized. One thing people certainly don't enjoy is being criticized in such a way that they are made to feel stupid. People can admit they are wrong, but they are very careful about how they are told that.
I'm not sure if any of this is relevant to the OP or not, but I can say this is definitely something that factors into my annoyance with unreliable people. The reason I bring this up is because ultimately, the only behavior and attitudes you can change are your own. I suppose it's possible to change those of others, but that's more work. I think, rather then trying to find some way to "deal" with unreliable people, you find a way to sort of accept them into the fabric of your life. There will always be unreliable people, so one might as well learn how to deal with them.
It might also help to have a calm discussion about it with the individuals in question.