I had my left kneecap dislocate about two years ago (non pole related).
I didn’t need surgery, but I did have to do physical therapy, and I still do strengthening exercises. I will get that stretching feeling you are talking about in that knee when I do splits. In my case it’s because my MCL has healed from being partially torn and is not quite what it used to be.
I hope I’ll get back to 100%, I don’t push it too far but I do still stretch, and have noticed increased flexibility in that knee over time.
Lastly, go see a doctor! I know why it happens to me and have a dr’s advice on how to handle it. It’s easier to prevent injury than to treat it!