If you mean "thin" as in insufficient shadow density that means the film is underexposed for the film/developer combination you're using. If you mean "thin" as in low contast, develop longer.(posted 8323 days ago)If otoh you mean both insufficient shadow density and low contrast, give more exposure _and_ give more development.
WARNING...this could also be the symptom of the "dreaded Xtol failure," which is a situation in which previously-good developer suddenly and unexpectedly dies, giving grossly underdeveloped negs.
Kodak has had some packaging problems with Xtol, so it's surely possible that you got two bad packages. I'd expect Xtol 1:1 to give 1/3 to 2/3 stop more "real" speed than HC-110 unless the negs were badly underdeveloped, and Kodak's recommended development time shouldn't be _that_ bad.
Another thing; be sure you used _at least_ 125ml Xtol stock per roll; significantly less than that could cause the problem you described. You may run into a solution-capacity problem with the Jobo depending on which machine you have; the CPE machines can't handle more than 600ml total solution.
Anyway...I happily used Xtol for about two years...and then suddenly got a grossly underdeveloped roll which was a throwaway. No more Xtol for me. While it has fine development characteristics otherwise, such a failure one day after the same stock developed film satisfactorily is unacceptable.
Lately I've been messing with a developer I'd never tried before, Ilford Ilfosol-S. It's a PQ/ascorbate developer in a liquid concentrate, which I use 1:14 in the Jobo to get sufficiently-long development times. Good speed, sharp, very fine grain etc.
BTW, try some of the new version of Ilford Delta 400. It's rather good.