Have you tried mixing another batch of XTOL or using FP4 with a different emulsion number? I'm a guy who also shoots a 'Blad and loves that film and developer combination--I'm afraid I just "gushed" about it in another post--so, like you say, we know the combo can work.(posted 9006 days ago)All I can think of is using bad XTOL, maybe some where Part A was caked, or bad film. I had some Agfa 25 once where the emulsion flaked off in big chunks, and I'm sure Agfa isn't the only manufacturer to have quality control problems once in a while.
When you do find out, would you post what you learned?