All sites hosted on same server started behaving like this without doing any changing/modification to the server.
When I try to upload an image to a WordPress site, it takes too long (5+ minutes) to upload and sometimes gets stuck.
When I try to open media library, the page does load and then a circle gets revolving again and again, it takes another 5-10 minutes to load the images.
The sites are hosted on Apache/Nginx dedicated server and I'm using latest version of WordPress.