@Fabio_P. Which FW region are these devices ? Here's how to determine that from the bottom sticker. Make sure that you're with the latest FW release on both devices. From your description I would say...

@quinzero Here's how to configure your RE. On your second question see this FAQ - Part 3 - Q3.6 In general you can daisychain 2 REs, but the bandwidth drop on the second one would be substantial and...

@oran469 What's your Internet connection type PPPoE or Dynamic IP ? Do you mean that if your modem is in bridge mode and Archer C80 is the main router, only then you have this issue ? If taht's teh...

@Dagless Since you're using POTS you need your telephone line (copper wires to your home) checked by your ISP to be sure that the signal is at its optimal level.

@Labib_T_Alam If your device is provided to you by your ISP then contact them to be advised further. This model FW has been customized for ISPs.

@Jondas Would you mind tell us what's the make and model of these problematic Android devices ? Meanwhile try first post suggestion from this thread and see if there's any improvement.