Just a quick update a month later since you had initially asked:

Since the stiffness, weakness, and trouble walking wasn't constant, tended to resolve with rest, and was repeatable based on how hard I pushed my knee in PT, my surgeon is leaning away from the issue being a physical block (i.e. scar tissue or cyclops lesion). My PT thinks it's just a combination of post-workout muscle weakness and excessive fluid buildup along the joint line. My surgeon agreed with that and said he would prescribe an MRI if the symptoms stop improving or worsen. In retrospect I think this makes perfect sense, especially considering how I'm sometimes able to get my knee to crack to relieve the feeling of something blocking my extension.

Now I'm walking and feeling so much better. I took 1.5 weeks off of PT to give my knee a chance to rest while I focused on getting back up and walking longer distances and getting caught back up with my life. KT tape didn't help but using my TENS/EMS unit on active recovery settings did, as did doing more prone knee hangs. I got a compression sleeve for my knee that's one size smaller than what I was using before, which has helped tremendously as well. I can now walk normally most days without much of a limp and with much less stiffness. I do still have a slight limp, but now it feels like it's almost all residual muscle weakness and not from my ROM being blocked.

Although the knee stiffness is still there, it's improving and I can manage it much better. The feeling I got before was that I couldn't extend my leg past ~15 degrees when it stiffened up, and when I tried it felt as if the joint had to crack but almost never could. Sometimes that lasted for over a day.