hip flexor pain

I wanted to ask if anyone had suggestions for dealing with psoas pain, particularly on straddle planche progressions. Almost anytime I flex my hips with a straight leg they fatigue quickly and hurt. 

Flexibility doesn't seem to be an issue as can front splits and do the table stretch, but I appreciate I am a larger guy attempting to learn this at 96kg

Two things: Stretch and Patience.

Make sure you really stretch out the hip flexor as well as the piriformis before and after, holding each stretch for at least1 minute if not longer. reduce the impact and start slower - as soons as they hurt, stop and stretch. good luck!