Failover only works when you turn off one of the devices, but not when one of the internet goes down. Companies that provide internet come with a GPON and a router. When the fiber signal in GPON drops, the tp-link router does not activate the backup link, as it identifies that the device is still connected. If I physically turn it off then yes it activates the backup link. Is there any configuration to resolve this? 

Remembering that this also happens with other models such as the TL-ER7206.

Thanks in advance for your attention!!!