Why does Gitlab throw a 502 error after a while?

Question

ubuntu

Good day to all
I installed the Gitlab server on Ubuntu Server 17.04, on the server 4 GB of RAM, 8 GB of SWAP, intel celeron 2 cores at 2.8 GHz.
Installed everything according to the official documentation.
The problem is that after some time of work or immediately after the commit, the server gives an error 502, the gitlab-ctl reconfigure and gitlab-ctl restart commands do not help, only restarting the entire server helps.
/var/log/gitlab/nginx/gitlab_error.log and ~/nginx/error.log are empty.
What is the problem and how can it be fixed?
Thanks in advance for your replies