Potential data to back the theory that it's all muscle imbalance related.
I was watching some Youtube stuff so as I could vary my routine without input from the physio, and out of curiosity tried some "clamshells". They are supposed to target the glute medius, and I have heard that's a muscle that cycling doesn't really do much for. On my left leg (the good one) it was easy to activate the muscle and use it to move my leg around - on the right leg, no matter how I was positioning myself, I either got groin involvement, lower back involvement, psoas involvement, or some combination of all 3. So I'm adding clamshells or other glute medius exercises, with the aim of firing that muscle and getting it working properly again - hopefully that can take some of the load off the stuff that's causing me pain.