Saddle biting you?
Bike fitting is a fairly systematic process usually, moving through the contact points and making sure that some critical issues like saddle height are in the right range before moving onto finer details like handlebar roll and such. Occasionally, though, something screams at me from the moment I look at the rider on their bike. I did the physical exam for a rider recently -nothing wildly unusual in her symmetry, strength and flexibility assessment but the moment she got on the bike she humped her back as if trying to escape touching the front point of the saddle.
I have seen this a few time with riders, more often with women than men, but the fitter needs to change the saddle before anything else can be done. Their aversion for pressure on the perineum(blokes) or soft bits(ladies) wrecks their posture on the bike, with low back flexion and often a serious amount of tension in the hip flexors when pedalling. Finding the right saddle (which probably will be a “hole-y” one) will put these riders on the path to comfort and efficiency.