Rstudio-server instance hanging for users.

We have rstudio-server instance on load-balancing with two nodes and head nginx.
We've seen many incidents from users struggling with Rstudio hanging/disconnecting.
We observed two error prompts:
"Unable to connect to service"
"Waiting for available socket........Error: Unable to establish connection with R session"

Those are happening "randomly" for users.
Could you please advise us in troubleshooting such errors?
Is there any limit of linux websockets that could cause such problems?
Maybe nginx on head should have particular configuration?