You didn't mention what your water-quality is. I suggest making two changes:
1. Mix a new batch of XTOL using distilled or DI water. I shake it to dissolve in a *capped* 5L container (with say 4 or 4.5L in it) to avoid adding more oxygen. Top it off to 5L after dissolving.
2. Pre-soak the film for 4 minutes before developing. I find a pre-soak gives Tmax-400 more density, and maybe that'll help Tmax-100 too. I doubt it would make a difference with the Ilford film though.