Alarm Module Press 1 to Acknowledge Issue

Ignition Version 7.9.4
Windows Server 2012 R2
Voice Notification Module 4.9.1
Alarm Notification 4.9.4
TTS Voice English 3.8.2

At one of our installations, we are still experiencing a remote voice call acknowledgement issue with the voice notification module. Upon answering the dial-out, when the notification module prompts the user to “PRESS 1 TO ACKNOWLEDGE” the ignition notification module does not acknowledge the active alarm. The module simply hangs up the active call. However when the notification module prompts the user to “PRESS 2 TO IGNORE” the ignition notification module does reply with an acknowledgement that the “2” key was pressed with our pre-configured text string associated with the mobile voice line user’s “2” key press.
We are having trouble determining from the notification logs why a “1” keypress may be ignored?? We would’nt expect the users roles / permissions model to be associated with this issue?? All pipeline configurations are set to allow that “On Call Roster” to have permissions to acknowledge a voice alarm. We have an unrelated “working” site using the same exact hardware and voice modem, so we are suspicious of the telephone system carrier side being part of the problem. We have a desire to modify the voice module prompt to use some number other than “1” as a test, however there seems to be no gateway side developer access to modify the key press variables. If any of you forum users have experienced this issue, and found a solution, we would greatly appreciate direction you could offer.
We just found the updated Voice Notification Module “4.9.4” may have resolved this bug
Thank you, we will figure out how to withdraw a post soon:)