When I add a new variant, I get a notif that it was added, but the page tree doesn't show the added variant. I have close and re-open the parent node (or cause some other state change) in order to see the newly added variant (in the screen shot, I actually added two because I thought it didn't work the first time round).
Likewise when I delete a variant: I'm asked for confirmation and get the confirmation notif, but I only get to see the deleted variant when I close and re-open the master node.
This issue has been detected on a 5.3 snapshot release.
I suspect this may have to do with us backgrounding some tasks. Both the add and the delete action take less than 5 seconds to execute, so they shouldn't be run asynchronously, but at least in case of the delete, I can see the following log entry: