fwiw:
I too would say its brass being too clean from the wet method. The times I have wet tumbled, once the cases were dry. . . I run them for 45-60 min. through corn cob treated with nu-finish & mineral spirits, cap here & there depending on the times/cases tumbled. I spray with Dillon case lube/spray, haven't had an issue with cases sticking to the drop or die.