Hi, I am 9 and 10 months out from two successful TKRs. My story and history is very similar to yours. I continue to experience stiffness and soreness, daily and am active. It is not debilitating, annoying yes.

I spoke to my surgeon's Nurse Practioner about this just yesterday. She stated this is a condition to be expected, more ongoing than not. Recommending to continue strengthening stretches first thing in a.m.. , brief icing/elevate, as needed, and Tylenol, GABEPENTIN.
I see my surgeon for my annual in a few months. I will ask more then. Note: I had expected TKR to relieve all my symptoms, although overzealous in my expectations I am still thrilled with the outcome.

I wish you improved wellness in your journey