HC-110 and T-Max do not seem to "like" each other, but I've never had the mottling problem you describe. Plain old D-76 is actually the best developer around for T-Max films, any format.

When using HC-110 and any B&W film, in any format, Dilution B is waaaaay too strong I find. Weaken your solution and extend your developing times. It's a small possibility that too high a temp and too strong a solution of HC-110 *might* be the cause of your problem. Hard to say.

good luck