RSS import hanging in WP Admin, zombie PHP processes appear

I am unable to import RSS feeds via WP Admin. I load content to my site by creating a WordPress WXR RSS file on my local machine then import via WP Admin.

When I go to the page:
https://site/wp-admin/import.php

and click ‘WordPress’ (the last option), this link:
https://site/wp-admin/admin.php?import=wordpress

I do get the page that stats:
“Howdy! Upload your WordPress eXtended RSS (WXR) file and we’ll import the posts, pages, comments, custom fields, categories, and tags into this blog.”

but the browser status bar is still chewing like it’s waiting for more data though the page looks like it has fully rendered. I’m hosed at this point, I can’t get to any other page in WP Admin and can’t to the blog at all. This happens in all browsers (IE, FireFox, Chrome, Safari).

This action also seems to create zombie PHP processes on the server (linux).

I whack the PHPSESSID cookie and I am able to proceed with the import (figured this out during troubleshooting so I have a workaround) but there is clearly something wrong. The site and WP Admin otherwise behave fine if I do not go to this offending WP Admin page. I got no complaints from users and traffic to the site is the same so it’s not affecting things overall. So it looks like somehow my session gets in a bad state.

I’ve done many imports this way in the past with no problems but this just started happening recently. I’ve done nothing to the site and made no changes to the DB/PHP files/plugins or otherwise so I’m not sure what’s going on.

Any insight appreciated.