The message you are likely to see is as follows:

Regex-optimize memory use (40, 0x10000/0x1000000) " 0 E000F:65 jit_mgmt.cpp:334

This is an internal message and is meant for engineering diagnostic purposes only for a new regex optimization feature. It does not cause any performance impact.
It will be logged upon reboot and when WAF policy is loaded or policy install occurs so if you are doing frequent policy installs then you will see the message being logged.

Please ignore this error. It is an internal message and will not be sent via syslog or email.