Firmware version: Any
Extension A dial external number via SIP trunk, after call established, extension A transfer the call to extension B. But the call between external number and extension B has not been established.
Log captured by Asterisk CLI. Here is a notification on "t38fax" which means the call flow has passed the context of T.38.
Disable "T.38 Support" option on outbound route setting.
If the T.38 is essential for usage of your scene, you can create one more outbound route and enable T.38.