Ancient Vows - Cannot Complete

I have both pieces to complete the quest.

However, when I move my cursor to my inventory the relic disappears and will not let me move the pieces.

I have relogged and changed servers, same issue.

I am less concerned about not getting the reward for this mission as I am with quest items not able to be moved into my stash.

This means that 4 slots of my inventory are permanently taken by these pieces.

If someone is able to help, I would greatly appreciate it.

Same here. Cannot finish the quest. The right half of the kabala clan relic is already slotted in the altar, but I cannot put the second half into it. The altar stash only appears, when my mouse coursor hovers over the altar itself. But not, when I have picked the relic from my inventory. Then just nothing happens.

Ok, the trick seems to be, before you are able to put the relic to the altar, you have to activate the seals again (what you maybe already did, to open the titan grotto). Anyway, you may have to do it again. Worked for me.

I was experiencing the same issue, and I found that turning on the "always highlight" setting under interface settings fixes the issue.
P.S.: Don't forget to save the setting