If session.save_handler is set to files, on systems that have maximum path length limitations, when the session data file's path is too long, php may get you an error like "No such file or directory" and fails to start session, although the session-saving folder really exists on the disk.
You should:
1. Keep the session-saving folder's absolute path not too long
2. If you're with PHP 7.1+, don't set session.sid_length to a number too great, such as 255
I once got stuck with this problem on Windows and wasted hours to solve it.
