Thumb buttoons no more work with Push to talk

Before some weeks (and more than a year before) i have my voice button at the 4-mousebuttom (thumb buttoon) - this dont works anymore. I have tryed use a other button and than go to my prefer button back but the mousebuttons dont detected from discor more.

Have no chances in my drivers, Hardware or some else and the mousebutton itself are ok - in Teamspeek it worked perfect.