I'm wondering if maybe you have torn the Sartorius? It seems you have been attacking it quite fervently with the stretching and physio/sports massage, but it isn't letting go completely. Giving you pain 20 mins into a bike ride seems to me too soon for tightness. If anything, I would suspect that the tightness would disappear as your legs got warm and you would present with a painful at the start and the end of the session, but nothing inbetween sort of thing. Have you had any imaging such as anMRI done to look into the physical condition of the muscle. Could possibly be a grade 1 or 2 tear and that is giving you issues.