I do apologize I just tested this on multiple pages with FF, I.E., and Chrome and I am not rerproducing this issue.
This error seems to have returned with the April 16 update.
Related Content is displaying a white box pop up when mousing over
referring presumably to ticket PRE-1976
This error has reappeared with the March Site Update
as can be seen for example by mousing over the "related content" items at: