OP, has your conditioning changed? Hamstring looseness? Have you ridden in cold weather with warm knees? ANd especially, have two or three of these occurred at the same time?
I was diagnosed with CP, chrondomalcia patellae, after I did a 100 mile ride on my racing bike early March in Massachusetts wearing the same clothes and shoes I wore and raced the year before. Difference was that I had a head injury and massive lose of conditioning late the previous fall. I also switched from my short cranked fix gear to 175 cranked racing bike. That started my journey with CP that has continued to this day.
Take a look at
https://www.bikeforums.net/recumbent...speed-gto.html post
#12 . I posted what I wrote for another forum near 20 years ago about my experience with CP and the excellent advice I was given by a sports ortho surgeon. (Sometimes you get far more than what you pay for. That surgeon diagnosed me for free in the back of a van following the first race of the season that I had to drop out of due to the above knee issue, now 3 days old. That doc was a competitor in the race. Race promoter introduced us.
I am not saying you have CP. But if you do , it isn't going away. Ignoring it will take you to a knee replacement. Good thing is that the new titanium ones are pretty good, unlike the choices 40 years ago.
Oh, every ortho I've talked to since that day has told me the advice given to me in that van was right on the money.
Ben