admin-ajax.php 502 response after update to 8.8.5

hi
I have
– WP Cerber Security 8.8.5
– WordPress 4.9.17
– php 5.6

When I try login from front to https://apartik.com/wp-admin/admin-ajax.php
I get response with Status 502
In server logs I see next:

2021/05/16 13:59:17 [error] 639#639: *526144 upstream sent too big header while reading response header from upstream, client: 185.11.28.202, server: apartik.com, request: "POST /wp-admin/admin-ajax.php HTTP/1.1", upstream: "https://45.76.87.13:8443/wp-admin/admin-ajax.php", host: "apartik.com", referrer: "https://apartik.com/"

but in cerber-traffic I see my login with HTTP 200 OK code

16.05.2021, 12:54	/wp-admin/admin-ajax.php
POST HTTP 200 OK IP in white list

Previously, when updating to 8.8.3, there was also this problem, which is solved through:
https://www.ads-software.com/support/topic/i-have-problem-with-admin-ajax-php-after-update-to-8-8-3/
But now everything works only if I disable plugin WP Cerber Security

The page I need help with: [log in to see the link]