When trying to address such complex interrelated physical issues as you have described its often difficult to find and to focus on the key elements that is the source of the problem. It works best to address one problem adequately and then, as other areas may become symptomatic work on these. It’s a bit like peeling an onion where there are many layers. (this is why you may feels as though it’s a moving target!)
It seems as though addressing the knee muscle imbalance has been helpful so that is a great start. My advice is to continue to do your knee exercises at a maintenance level, always do your abdominal stability exercises and then start working your way through to the next problem.
It seems to me that your left piriformis may be very tight and or in spasm causing the left buttock pain. This will disrupt the functioning of thesacroiliac joint so it would be good to have your physio check out this area and mobilize it properly. This cant be done adequately online or without some hands on work. Often the asymmetry starts from the pelvis, which then affects up and down the spine.
You may find that once part of your problem eases then your whole pattern of symptoms change so don’t lose heart it just means that you haven’t got down to the bottom layer yet. Often the deepest layer is due to an old injury that has set off trail of responses in your musculoskeletal system ie weakness on one side, tight muscles avoidance of weight bearing on one side.
Don’t forget to work on your posture and balance also and do general exercise such as walking or swimming.
Some questions to ask…
How long have you been getting symptoms? What started ? and how old are you and what is your normal level of activity?