oceanspruce,
I had severe pain in a similar area after TKR and there was an orthopedist who was going to excise my popliteal tendon and he wrote in a patient portal that he had told me that I could be worse off however he had never told me that so I cancelled the surgery. I am glad that I did cancel because I went to another Orthopedic Clinic and they did an ultrasound and saw right away that I had what is called a fabella bone. This is a fairly rare bone that not everyone has and not all doctors are looking out for it. Sometimes after TKR this bone can cause a lot of pain. I could feel a little lump under the skin.
I had surgery to remove this bone and it immediately took the awful pain away.

I thought I should share this with you since your issues sound similar to what I went through. Maybe you could get an ultrasound to see if this is a possibility.
Katrina