Your issue might not be about fop2 but most probably your sip configuration. Do the test, call to one of your trunks, then run
asterisk -rx "core show channels concise"
Take not on the channel names.
Then hangup that call and dial the other trunk/inbound route, and check channel names again:
asterisk -rx "core show channels concise"
How do the channel names look like? Many times, incoming sip peer matching is not well resolved and the device name won't be the one you expect to be. Maybe you are having that issue.
Best regards,
