Session problem?

Question

PHP

Suddenly stopped logging into the CMS admin panel
When viewing the logs, I found

[29-Jun-2021 13:46:00 Europe/Moscow] PHP Warning:  session_start(): open(/tmp/sess_e7425020a35d22b683155324c4930a24, O_RDWR) failed: No such file or directory (2) in /var/www/data/www/backend/index.php on line 10
[29-Jun-2021 13:46:00 Europe/Moscow] PHP Warning:  session_start(): Failed to read session data: files (path: /tmp/) in /var/www/data/www/backend/index.php on line 10
[29-Jun-2021 13:46:00 Europe/Moscow] PHP Warning:  Session expired in /var/www/data/www/backend/index.php on line 28

Actually swears at the line session_start();

There is a tmp folder in the hosting root, and the rights 777 are set on it. And it happened suddenly, before everything worked.