404 after login to dashboard (after 4.4.1 upgrade)

I’ve tried different methods to fix it, such as disabling all plugins, clear Cloudflare cache or clear browser cookies with no success.

Also try:

– switching to the unedited default Theme (Twenty Sixteen, etc.) for a moment using the WP dashboard to rule out any theme-specific issue (theme functions can interfere like plugins). If you don’t have access to your admin area, use FTP , or your web-host’s cPanel or whatever file management application your host provides (no Dashboard access required). Navigate to /wp-content/themes/ and switch to the default theme by renaming your current theme’s folder by adding “-old” to the end of the folder name. Alternately, you can remove other themes except the default theme. That will force your site to use it.
– If all the above steps do not resolve the issue, then try MANUALLY updating. Download a fresh copy of the WordPress .zip file to your computer, unzip it, and use that to copy up all files and folders EXCEPT the wp-config.php file and the /wp-content/ directory. You may need to delete the old wp-admin and wp-includes folders and files on your server before uploading the new ones. Read the Manual Update directions first.
– Backup: If you haven’t already done, always backup everything (including your database) before doing any actions, just in case something really goes wrong.

Thanks for your answer.

1 Switching to the default theme (2016) didn’t work.
2 A manual upgrade didn’t fix it neither
3 The only thing that worked was to downgrade to 4.3.2 (and that’s not a real solution)

It seems clear there’s a conflict between Mod_Security and WP 4.4.1. If Mod_Security is on, WP fails at login (404 error), but if it is off, WP works as expected.

It seems clear there’s a conflict between Mod_Security and WP 4.4.1.

yes. So the best is to contact the hosting provider.