Websocktets gets ignored after 3k concurrent requests though the system usage is less than 35%. Any idea on why this happens

Please suggest overcoming this

How many parse server running on the server? Maybe you should double the running instances. Or maybe you hit the open file limit? Every connection opens a file( I don’t know if this is the correct word) .

I would try doubling parse server first. For example if you run 1 parse server in the server run 2 parse server.

Try this:

Edit the file on your Linux system /etc/security/limits.conf, add:

* soft nofile unlimited
* hard nofile unlimited

* soft noproc unlimited
* hard noproc unlimited

* soft stack unlimited
* hard stack unlimited

save and reboot, then see if fixed your issue.
If not, try @uzaysan tip.