Yes, it is incoming call to CUCM from expressway (originated from Skype for Business) and terminates at SX20 video endpoint. Yes, there are SIP route patterns for outgoing calls in CUCM to expressways. There are no issues with outgoing caller identification.
The issue is only for incoming calls to SX20 where it changes the email@example.com to firstname.lastname@example.org where 100.100.100.100 is the cucm ip. Because of this, we cannot use the missed/received call information to dial the caller back.