Asterisk.c, "Too many open files"

About once a week, the asterisk process goes into a tight-loop (100%cpu), stops responding, and fills the file system with these syslog warnings:

  **WARNING[1100] asterisk.c:  Accept returned -1: Too many open files**

asl-asterisk 1.01-20180226-9

I’ve upped the ulimits on open files, but it’s still an issue. This system gets very little traffic fwiw. I moved the log to a ramdisc to protect the sd card, and setup a nightly reboot. is there anything else we can do?