LTM logs to Cortex XSIAM are unreadable

Hello, I am trying to forward F5 LTM logs to Cortex XSIAM. We have an on-prem broker for XSIAM and the logs are to be forwarded to the cloud. Data flow is: 

F5 -- Broker -- XSIAM

We are able to see the logs but for some reason they're unreadable. 

We followed the steps outlined in this link on the cortex official site. 

Please, any idea what could be causing this?