https://techdocs.f5.com/en-us/bigip-14-1-0/big-ip-asm-implementations-14-1-0/logging-application-security-events.html
About logging responses
If you enable response logging in the logging profile, the system can log only responses that include the following content headers:
- "text/..."
- "application/x-shockwave-flash"
- "application/sgml"
- "application/x-javascript"
- "application/xml"
- "application/x-asp"
- "application/x-aspx"
- "application/xhtml+xml"
- "application/soap+xml"
- "application/json"
The system cannot log other responses.
If your response have the "application/json" then system should log the response.
The manual for v12.1.x says the same.
Cirrocumulus