I often cook chicken thighs in my InstantPot pressure cooker, 12 minutes on high with a marinade and it turns out tender and perfect each time.
This time, however, the thighs were still a little frozen. I had let them thaw for 2 days in the fridge, but I could tell when I squeezed them that they weren't thawed all the way through.
I put them in the InstantPot for the same amount of time with the same settings, and they came out quite tougher than usual (but still done all the way through).
My theory is that it took the Instant Pot longer to get to pressure due to the temperature of the chicken thighs, and so ended up cooking them longer...
What could be the cause of the dramatic difference in toughness?