su: /bin/bash: Resource temporarily unavailable
Just restarting postgres is not a long term solution, you will hit the limit again, unless you have physical resource constraints on the server such as memory. During the issue the number of processes opened(nproc) by postgres user was 503 and the estimated number of open files(nofile) was 35225 and yet your postgres_limits.conf shows that you have set nproc to only 400 and nofile to only 4096. Based on your data, you will need to increase those two parameters.