Heck i'll join in on this. After my third knee surgery in december i started having this very problem about a month ago. Happened during a 30 mile ride, I ended up having the wifey come get me.
Im 2x physical therapy right now as well and doing some of my own exercises at home that dont involve load bearing on the join. Like the SL Lifts.
Though, I am having additional symptoms not mentioned here. Popping and clicking!