TVHM - Last step "place eridian"

Hey,

im stuck at the very last step after beating tyreen. Tannis wants me to put the stone in the mayhem thing (sorry i play on german).

But it doesent give me credit for putting it there so im stuck in the last queststep on TVHM -.-
Any suggestion?

Its my 3rd character and the other 2 runs were fine.