FreePBX achieves certain calling features by manipulating SIP headers on the channel at various places in the call flow. There are two SIP drivers, and there are separate dialplan applications for adding a header depending on whether it’s a sip or pjsip channel. Freepbx uses both applications to add the header, and since the channel can only be one or the other, the result is that one will succeed and one will always fail and log a warning.