Research Book Glitch (Please help)

I had a full inventory and I wanted to pick up an item but clicked on the research quest book. It disappeared bc it tries to put it back into my inventory but failed due to my full inventory and now it is missing.

 

If it's a quest item you can just do /fixquests and hopefully you'll get it back.
If your inventory was full and the item really disappeared then there's sadly no way to get it back. What the server normally does is it instead drops the item on the ground, but if that didnt happen then theres sadly nothing you can do