3-way Merge disconnects callers after Merge to Conference button is pressed

This is a problem in the Softphone App. We are having an issue where our users attempt to make a 3-way call, sometimes called Local Conference, or 3-way Merge, where we are on a call, click to add a user, dial the number using the dial pad, connect successfully to that 3rd number, click on the Merge To Conference button, then both callers are disconnected about 1 second after the merge to conference button is pressed. Is anyone else having this problem or heard of this problem. This is getting very frustrating to diagnose.