Now I stumbled to even more interesting case. The same issue occurs also in back-end form list when hovering on the form label right after refreshing the page.
But it does not occur in back-end list table. And I noticed that the form label in the backend has a
"popover" tooltip, but the list label where the issue does not occur, has a regular html tooltip.
So it seems to be related to the "popover" tooltips which maybe adds "display:none" to the wrong element when the dom has not yet loaded fully.
EDIT: and when the element label in front-end does not have tooltip, this issue does not occur, so everything points to loading of tooltips.