At a faster cadence, you may have reduced your pedalling force to a smaller area/angle and if you’re keeping the same total power output as before, there will be increased torque there, too.
Slow pedalling generally uses a wider angle/rotation of power. Fast pedalling generally (not always like not in an acceleration) may rely more on outputting power during 12 - 4 o’clock and that’s where you may be kicking your lower leg forward much more than before—putting more strain on your patella tendon.
You can try to modify your pedalling biomechanics over time, or at least be cognisant of it. You can try an online/app or in-person fit. You can also experiment with trying to activate your glutes and other muscles more with different pedalling drills. Perhaps start with a slow 50rpm cadence, being mindful of applying pressure all the way around and activating all those different muscles, then go back up to 80rpm and see if you can still sort of use most of them. The only concern with a perfectly consistent pedal stroke is that it may not actually be as effective as something that doesn’t look so elegant. However, at least you’ll start to make a mind-body connection and develop something that uses maximum muscles with minimum thought.
My guess; Your change in cadence caused you to change your pedal stroke a bit. This put some pressure on your knees that they were not accustomed to. I would stay at a comfortable cadence and slowly work up to spinning faster. Your muscle memory will adapt it just does not happen overnight.