Why does PhpMyAdmin work every other time?

Question

PHP

Good afternoon! There is a bunch of nginx php5.6-fpm
phpmyadmin is installed on this server. When I go to the address, it normally shows me an authorization form, after successful authorization it shows me a list of available databases, but as soon as I send the next request to the server, it doesn’t matter how, I refresh the page or click on some link, that’s all, the application freezes, and as a result, the 504 status returns to me. After that, if I click on refresh the page again, everything works fine. And so in a circle. That is:
the request is normal
request 504
Looked, the following error is in the logs:

[error] 2767#2767: *43168 upstream timed out (110: Connection timed out) while reading response header from upstream, client: 11.101.3.158, server: pma.domen.ru, request: "GET /index.php?token=71fe8336d611f962020905ce82cc5c0f&ajax_request=true&ajax_page_request=true&menuHashes=38a75883&_nocache=1600070056729586276 HTTP/1.1", upstream: "fastcgi://unix:/var/run/php5.6-fpm-pma.sock", host: "pma.domen.ru"

Previously, everything worked fine, but when the Internet access was cut off from the car, such glitches began.
What could be the problem?
Thank you very much in advance!