WordPress displays 404 after publishing post, changing settings, etc.

Since the last 15 days or so, whenever I go on to publish, schedule or edit a published post, after I click on the button, the animation near the button freezes and does not move. The circle animation in the tab moves in circle.

The pages stays this way for literally 1-5 minutes. After that, I see the 404 Page Not Found Error Page.

At the end of this, the desired action may have been carried or, or not carried out. But a 404 page is seen in either case.

This happens even I edit a user or activate or deactivate a plugin or change some settings in the WordPress panel. But posts get saved as Drafts.

This happens randomly. At a stretch I may be able to work, while at other times, this keeps happening.

I have installed no new plugins. Only update WordPress and plugins to latest versions. I uploaded freshly downloaded WordPress files. I have also tried it with the default theme. I have disabled all plugins and tried, but still face this issue. I even changed the post draft auto-save time interval from 1 minute to 5 minutes. It did not help.

I use MaxCDN, which has been configured correctly and checked by their Support. In any case the CDN does not cache the php or admin pages.

I’m the admin and only I face this problem as I have editing publishing scheduling rights. Other authors do not face this problem.

Any ideas why this is happening and what I should do to resolve this frustrating problem? I have read the other threads here, but they haven’t been much help.