4.4 upgrade: users can't login

Can you provide a URL to your site?

Main site: https://svj.hu.nl/
Sub site: https://svj.hu.nl/propedizzy/

I would recommend “deactiving” all the plugins. You can do that by renaming the plugin directory. You might want to manually re-install WP.

Deactivating the plugins and reinstalling 4.4 doesn’t help.

Downgrading to 4.3.1 gives blank pages.

You should turn on debugging to see what is going on – https://codex.www.ads-software.com/Debugging_in_WordPress

Downgraded to 4.3. We are able to log in again.

I had exactly the same issue and had to revert to 4.3.1.
However before reverting I found out that by disabling SSL for admin in wp-config and changing the URL protocol to https:// then I could login.
Reverting to 4.3.1 is not a fix nor is disabling SSL.

Just in case it helps someone I discovered that my problems were caused by an out of date plugin in my mu-plugins folder.
Updating the plugin (more privacy options) allowed succesful upgrade to 4.4.

Sounds good gzu! We use the plugin too. Next week (holiday for most users) I’ll give it a try.

Had a similar issue with WP 4.4 which caused an infinite loop somewhere during the login process. It only seemed to affect new people wanting to login as existing login cookies worked fine. The apache threads never end and thus end up killing the server.

Turns out it wasn’t a plugin issue. We dont use any mu-plugins. Reverting to 4.3.1 was the only thing that fixed it. Managed to narrow it down to something inside of wp_signon.

Updating the plugin More Privacy Options to 4.1.1 and deleting the old version by FTP cleared the way to upgrade WordPress to 4.4.
Thanks all!