Mike, many of the rest of us tested Xtol with our film before committing to using it and then got bit when it inexplicably failed completely.(posted 8419 days ago)As to thin negs, it probably is not an Xtol failure but either underexposure or underdevelopment as mentioned above.
Do you know how to tell if the negatives have received full exposure by looking so you can tell if it is only underdevelopment?