Can't do leg extensions 6 months post surgery

Hi everyone, I got surgery with quad graft 6 months ago and I still can't do the leg extension machine

At about 30 degrees I have friction on the outside of my knee and if I go past and force through it it's very painful and aggravates my knee, I feel like something is wrong

On all other exercises I don't have any issues as long as it's not the same mechanics as leg extension (e.g. holding pushup position hurts my knee if I straighten my leg)

I talked about that with PT and my doctor like 2 months ago they told me it's probably inflammation and that I need to be careful with quad exercises and that it should get better later on but now I feel better but I still can't do these damn leg extensions

I feel like this makes me late in my rehab as I can't easily target my surgical leg quad, I don't feel it on other exercises

If I try to do only the beginning of the range of motion at leg extension, I can barely move 18kgs with my surgical leg when my non surgical one can lift 52kgs full range of motion for multiple reps

Did anyone have the same problem ? any insight ?