This is an issue/bug that will appear when one of two things or both are present in a list view: The total number of records found and the number of rows visible in the list view. Increased found set and/or more rows showing will make this appear. To test that this is true (not a solution!), try increasing the row height or find a smaller found set.
Note that the problem will not go away if you remove fields or items from the body. You can duplicate your layout and remove everything except the pop-over, and the issue will remain.
Once the problem happens, you can fiddle around with the layout and maybe sometimes get it to work, but there doesn't seem to be a real formula for how to prevent it. Sometimes we get a found set with 10 rows showing on a typical screen to work, other times not. Sometime it will work on one monitor, but fail on a higher resolution monitor.
Edited for clarity.
what do you mean by "The total number of records found and the number of rows visible in the list view. Increased found set and/or more rows showing will make this appear" ?
I tried the following: The list view has a filtering, but yesterday I was showing all the records and clicking on the pop-overs. Today I tried on a sub-set of the records by filtering them and it worked !! Magically all the pop-overs were clickable as before.
"Today I tried on a sub-set of the records by filtering them" = Total number of record found. Same thing. It's not all records vs a found set, it's the total number.
If your table had 20 records, then any found set would work. If you have 2,000 records in your table, then only a subset will allow pop-overs to work, and usually that number is less than 50.
"the number of rows visible in the list view" also helps determine if your pop-overs work. Taller-sized body parts will show fewer rows per screen. Show 20 and your pop-overs fail. Show 10 and they may reappear.
Also, pop-overs are not the only feature to fail. Row highlights will fail as well.
I've noticed that in addition to the pop-over failure, the row highlight fails as well. If you watch the elements in your browser developer tools, you will see that clicking on a row still does in fact change the class of the row from "v-table-row" to "v-table-row v-table-focus v-selected" as expected, but the row does not render any differently on screen.
This was important to me, because although I didn't really like the idea, I thought perhaps I could make a work around by moving the pop-over to the header. I replaced the pop-over on the row with a "Go to object" button, which opened the pop-over in the header. The header pop-over worked consistently, but I found it would be potentially too confusing to the user. When row one is highlighted as the active row, but row five is actually the active record, and the record that is showing data in the pop-over, you are just asking for trouble.
I'm hoping this gets sorted out in a coming update.