What about the light status when you get the error message? BTW, did you test the wired connection or not? I mean connect your computer to the router by cable to see if it's stable?

I am afraid there is no more detailed report, I don't see that either...

it doesn't have https admin page, hope it could be added in the future

You may try the factory reset again: with the extender powered on, press and hold the reset for about 10s until all the lights flash once and go off, then connect your device to the extender either...

So strange, the extender shares the same SSID as your router or not? anyway, since the 5G of the extender works, it should be connected to the router, you may call tplink support or email them for...

I checked that already, the monthly report only appears in the notification, and the Deco App needs user authorization to show corresponding notifications in the notification bar. It can be set up...