Nordic UART Service Stops Advertising


We are using the Nordic UART service.  Our project is based on the example project "ble_app_uart" from version 15.2 of the SDK.  I've found after about 3 minutes it stops advertising (the reason why I am unable to connect to it).  What would be the most likely cause?

If I connect to it before it stops advertising, it all works fine.  I can connect / disconnect again and again with no problems as long as I don't leave it sit advertising for too long.  When connecting to it I have been using the central example project (ble_app_uart_c) or an iPad with a custom application.  Both give the same behaviour.  As far as verifying if it is advertising or not goes, I'm using the nRF Connect Andriod App.