Tip for Githyanki Inquisitor Barrier
To place the shard after the fight, open the inventory of the toon carrying it. You will note it will overlap the top of the area where you place the shard.
Move cursor to very top edge of inventory screen of that toon and hold left mouse button and drag the inventory screen to the left to reveal the screen below it where you place the gem. Now drag and drop the shard into the slot to open the gate.
This drove me nuts for hours and I killed everything in the creche thinking that it was about me being in combat since the room lit red every time I reentered it.
Hope this helps those with this issue!