Is the grain sharp and the image mushy or is it a case of oatmeal-like grain?
I have had occasional similar experiences. I found some subject matter just makes the grain stand out - anything with areas of very smooth ZIV-ZV tone like a featureless blue sky and #25A filter or young darkish skin.
Sometimes the negative just comes out mushy for no reason that I can find. Sometimes the 'mush' turns out to have been camera shake and disappears when I re-shoot with a tripod. My suspicion is the other cases can probably get traced to bumping the focus, a poor seating of the focusing screen/ground glass, ditto for the film holder or back, buckled film
Oatmeal grain seems to be a function of film/developer combination - when it happens I stop using that combination and so my observation isn't statistically significant. Though I haven't tried it, I wouldn't have thought Delta 100/Xtol would be one of those combinations, but it might. TMax 100/Xtol is certainly grainless.