are you getting calls through a Call queue? if yes check the Admin Portal>Call queue > Call Handling > Wait Settings > Max caller waiting time in queue.
if this is "Don't wait" it will result in the behavior you are describing.


Another thing you could check is the Admin Portal > Users > Click on your name > call handling.
If you have added an additional mobile number (see attached pic) and that number rings simultaneously with your app, then if your mobile is set to send to voicemail, whoever called you is getting sent to the voicemail of your mobile, which RC interprets as the call being connected. The caller is now "speaking" with the voicemail and it therefore stops ringing to your app.