@DiagonalBike 

Firmware release do not always equate support ending on a product.  In most cases if a Firmware stable, there are no bugs or security concerns to address, or a feature is being changed then likely there will not be a new firmware released.  Baiscally if it ain't broke don't fix it.  We have not seen any updated recently about issues with the A20.  As to your questions these notifications happen anytime there is a change is  the WAN port status.  That could be Internet outage, the lost of the WAN IP and being assigned a new one, a power outage or power cycle, etc.  Anything that can affect the WAN port. 

To troubleshoot check to see if there is any change in the LED for the WAN.  Swap out the Ethernet cable between the modem and router and have the ISP do a intrusive line test to test the quality of the service.