LR has fogrotten previously tagged faces/people

A few days ago I was working in a collection using the search function to view some old photos of someone.

Yesterday I wanted to show them, so I went into the same collection, put in the name, but nothing happened, it was not in there, later I checked that the photos are still there but found out that the entire person with 1300 photos got its name removed and was untagged.

I reentered the name, but in this particular collection its still not showing up as viable keyword to search.
Just fron a quick check I could see at least 3 more people that got untagged, there is probably more..