I'm not familiar with this situation. I had success with having both knees replaced. Question – did you do all of the post-op stretching exercises – the ones that are boring, repetitive, and hurt somewhat? The only time I'm aware of scar tissue forming is if those exercises are not done. Anyway, you don't have to answer. Just be honest with yourself and your surgeon.
If you did all the post-op exercises, and I think you did because you say your ROM is good, this sounds like a one in one hundred problem where the patella prosthesis is not tracking in the groove in the femur or maybe the implant. I suppose that could cause scar tissue.
The last person to post seemed to have this problem and the scar tissue was removed with a scope. But if the underlying issue is an improperly aligned patella (or maybe a problem with the femoral prosthesis, then your surgeon is probably right and it's best to do another surgery to 1) remove the scar tissue and 2) fix the problem. I don't think this can be fixed with a scope.
Sorry, that's all I can think of. All the best to you in getting this fixed.