han_sip.c: Autodestruct on dialog 'firstname.lastname@example.org' with owner SIP/omnisip-outgoing-0000001a in place (Method: BYE). Rescheduling destruction for 10000 ms
Then you most likely have a 'stuck' channel in Asterisk. That typically occurs when the channel should be destroyed, but something is still referencing the channel. This is usually sign of a bug in some off nominal condition.
As it is, Asterisk 11.9.x is pretty old - over two years now - and bugs involving stuck channels have certainly been fixed within that time frame. I'd recommend upgrading to the latest in the 11.x series to see if that resolves the issue.