Hello team:
I realize this is not a major issue, but it remains an annoyance in an otherwise most excellent plugin.
I have tracked the issue to security settings on the server, in my case.
I am having a similar problem. Version 7.3.7. I do see a 404 error in the console for wp-admin/admin-ajax.php — which is strange because the file is there.
I have opened a ticket, but I’m wondering if you found a solution?