Incoming SIP call rings once then gets "stuck"

Incoming calls are transferred to the correct extension but when the user answers, neither the caller or answer-er can hear anything. When the answer-er hangs up, the caller is still in a call. It seems like the connection was not fully completed and both are stuck in some in-between state.

Sometimes the call works correctly. During testing, it worked correctly every time. A phone number was ported to the system today and now it seems to leave calls stuck…some of the time.

Any ideas on what to check?

What version? How did you install? Is this a distro install? We need a lot more info to assist you?

Sorry about that.

PIAF (Updated to latest modules)

Using SIPStation trunks (Three channels).
Two DIDs.
Using the built-in IVR.

Additional Info:

The caller picks an extension and they hear one quick ring back. If the extension is not picked up right away, the callback ring does not continue to ring.

If the call is going to work correctly, the ring back continues until the call is picked up.