hey, here is a useful link for you: https://www.tp-link.com/us/faq-1970.html TL-WR940N with firmware version 3.17.1 Build 170717 Rel.55495n or earlier (Hardware Version 3.0 or earlier not affected)...

hardly see your post.. try to check the model number? generally speaking, it states EU/US/UN sample after the model. hope it works for you..

is the firmware latest one? If it's not, update firstly. besides, try to change another wireless channel.. is this 2.4G or 5G connection speed? check the negotiation speed.. how about your...

Since you can get valid ip address from the router, try to email tp-link support to do some further troubleshooting.

What's the model number and OS version of the Andorid phone? Looks like you need to check the phone itself since other phone can successfully edit it. Did you install any new apps on this phone...

Did you add those devices in the blacklist? Can you get internet access if you connect your pc to Deco via a cable? Try to restart your Deco units.