You may want to look at your CTI Ports Locations and device pool as well, ensure that they are in the right DP and L which your phones are in.
I encounter the same problem with CUEAC => from pstn call to operator, after blind transfer, just a notification to the final internal phone and no call.
The blind transfer works from internal phone to operator to final internal phone.
Unfortunately I don't see the key in regedit : Computer\HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\Arc Solutions\Call Connect\Operator\Preferences\Default
Do I create this key? But there isn't path arc solutions...