To add to this, I got the problem for every single Lich I encountered. The "requiem UI" disappears correctly at the first attempt but bugs when the second attempt happens weither you succeed or not.
I got something that fixed it by sheer luck in my last mission, though.
Someone else got a Lich and attempted to kill them, after my encounter. They failed and the UI fixed itself, showing my second mod and restoring the rest of the UI.
Note that it happened when I was the host this time so it's not a client-only issue.