If I have understood the OP's thread he already had done one film perfectly then in the same evening so maybe an hour later or less he did another film and got nothing at all - not even any hint of the numbers etc that Kodak, Ilford etc put on the film.
Xtol may suddenly die although I had thought we'd laid that one to bed but die totally in one evening after working perfectly on the first film???
It surely has to be something else. I can only think of fix first but he is sure it wasn't this