In Q172 this bug was mentioned and it is funny that we all haved lived with this for many years ๐
If in the content of a hovercard is another hovercard trigger, the initial hovercard will be closed when entering the inside trigger with the mouse. You can see the bug with every differential hovercard which contains reviewers. But there are other cases too: For example if project descriptions use mentions.
I think this shouldn't be fixed server side but in the hovercard JS code, where we somehow should intercept mouse events inside hovercards.