We use SL6087 modems on two different networks. On the one network, the devices have will not always play the ring tone for an incoming call. This behavior started recently. We are on FW 7.52. The problem occurs even when our app is stopped. You can call the device twice and everything will work. On subsequent calls, only a beep, or no ringtone is played. +CRING is however always sent by the device, auto-answer works and the call is set up correctly.
To ensure that it is not something we set, I reset the factory defaults (AT&F0) and stopped the app (AT+WOPEN=0)
How can I get more information in order to assist the network engineers? Any other ideas what might be causing this?