Hello,
From my side it's impossible to reproduce your issue (I try to add to let one variant description empty or with space, and with a tabular product page), so we will need more elements to understand what's going on.
Can you provide a screenshot variant configuration page, the best way to do will be to have one which description works and one that doesn't.
Other things to check, do you have an override on your view : product/show_tabular ?
If yes, maybe your customization is linked to your issue ? Can you try to delete it (after have save it on your side ?) to see if that solve it.
Awaiting news from you.
Regards