What processing is the call subject to? E.g. provide the full log with verbosity set to 5, to show the dialplan execution. In particular, are queues, or ring groups being used?
Is the call from a trunk or an extension? Is the destination a trunk or an extension.
Your current behaviour doesn’t sound like the default, but for one combination of answers to the above questions, No ringback tone on outbound calls - #3 by tm1000 tells you how to solve the reverse problem of wanting to have the PABX fake the ringback tone, and you can adopt it to restore the default behaviour.