You don’t mention the version of FreePBX you are running but we can guess the cause; based on the timing of your message we are aware of a particular corrupt SIP packet attack which appeared in June 2020.
Please upgrade your SecAst to version 1.7.1 and your system will no longer be vulnerable to this attack. If you want want to send us detailed Asterisk/SecAst/Firewall logs we can help you confirm the cause and the resolution. (Please send by email, don’t post in the forum)