Have you tried checking & clearing/resetting some or all of the advanced WiFi settings for both devices (sleep mode ? or even wifi region code)

Is it rooted as you might want to boot into recovery, and try clearing cache. etc.

Check your router/firewall logs to see if it is rejecting your devices based on MAC or its i.p. ??

It stinks when ISP lock/block out user access to the router/modem - backup your apps & settings, and do a Master Reset on the device, and start all over clean - it's PITA but sometimes & very often, things magically come back - good as new or even better.