I had similar once.
A long shot, but I found that there was air in the calipers, despite continuous bleeding.
I wound the caliper pistons all the way in with a "G" clamp with the bleed nipples open, and loads of air came out.
A quick re-bleed (after topping the M/C up) and problem solved.
Worth a try, if not a quick test is to clamp off the flexis in sequence to help diagnose the problem area.
Clamp all 3 off in one go and see if you have a pedal pressure that will stay up. Then release one at a time - it is probably best to remove the rear clamp first because if there is no change then you have discounted both rear cylinders in one go....
Pete Wiseman; Cambridge.
Mopar by the grace of God