I should probably say this was on the pre bue server.

I was finishing up Chapter 3 on Scarlet Witch when I came across a bug with recovering the ancient tablet from the hand at the top of that tower. It let me pick up the tablet as normal and exit via the portal. The cinematic fired off as per normal, but when I came back to Avenger's Tower, it was asking for me to retrieve the ancient tablet again. So I went back up the tower from the way point and the mini map was indicating there was an objective there, but it wasn't. I logged off, waited about an hour and tried doing the mission again to the same result.