No Ringback on Calls Transferred Off-net

[WrongWayFeldman]

Cisco Unified CM Administration System version: 10.5.2.12901-1
I have two clusters where both use SIP trunks from the same carrier.
The issue is that ringback from blind transferred calls to an external phone number on cluster "A" is not heard by the calling party.
Cluster "B" works as it should. The calling party will hear ringback.
Also, if the call in transferred to an internal number on either cluster, the calling party hears rinback as expected.
This does not appear to be a media resource group or annunciator issue although I haven't tried resetting the annunciator.
Is there some related service that would need to be restarted or some configuration that needs to be verified?

Cluster "A" No Ringback Call Example
DN 1234 calls DN 5678.
DN 5678 presses Transfer key.
DN 1234 now hears MOH.
DN 5678 dials external number 9,1-213-555-1212 and then presses transfer key again to complete transfer.
DN 1234 now hears dead air until the external number answers call.

Cluster "B" Ringback Works Call Example
DN 1234 calls DN 5678
DN 5678 presses Transfer key.
DN 1234 now hears MOH.
DN 5678 dials external number 9,1-213-555-1212 and then presses transfer key again to complete transfer.
DN 1234 now hears ringback until the external number answers call.

 

[gnrslash4life]

I would check your CUBE configs and your trunk settings in CUCM for starters.

Certifications:
A+
Network+
CCENT
CCNA Voice
CCNP Voice

 

[DisasterMaster]

It's the same config between both sites. One site works and the other doesn't. I restarted IPVMS service which didn't make a difference either.