Odoo 15 CE randomly stop responding to any requests. 
Logs don't show any errors. 
This happens pretty rare, one time server worked for 40 days without restart, next time only 3 days. I didn't have much ideas where to look for problem. In logs I didn't see any suspicious activity. Just odoo randomly stops responding.  

My setup are 
nginx as proxy
odoo installed from source (branch 15 last update Jan 2), with website and shop modules.

there are some custom modules. 

When server hangs, there are no high CPU load, or high memory consumption. it enough to restart odoo process itself. 

Any ideas, how to catch reasons why it stops working randomly ?