I’m on mobile and my internet is out, so I’ll probably follow up with more later when I’m on my computer. That said, this is something I spent probably a year dealing with, and I’m pretty sure I’ve read everything on the internet to be read about it, and have some very strong opinions.
The very short version beat I can do is: it’s caused by either weaknesses or muscle imbalances, but that also manifests into extremely tight muscular fascia. Success for me came from both strengthening AND foam rolling
Specifically, this video:
I probably did those exercises hundreds of times. But also, I found foam rolling absolutely crucial. I know, I know, the ITB is a tendon, you can’t stretch or roll it, I know. Buuuuuut the tendon doesn’t exist in isolation. Foam rolling and crossovers stretches were nearly tears-of-joy inducing. My quads and glutes were just completely knotted up. Rolling was excruciating the first few times. Once everything relaxed, combined with my new strength to keep my form in place, everything has been lovely ever since.