@Paqueiros forgot and register again wifi network in android devices. 

@Paqueiros

Same issue as mine here https://community.tp-link.com/en/home/forum/topic/170848

My ISP router wifi (NOS Hytron) also works fine and I have the main deco connected in bridge mode.

I only have major issues with several nokia 2.2 (can only connect to 2.4Ghz), all other devices (laptops - 2.4Ghz or 5Ghz, printer - 2.4Ghz, tablets and several different mobile phones - all in 2.4Ghz) "seem" to be fine (it may be that they also have issues, never ping'd those in fact, but if they do there is no visilbe issue and they never disconnect). The nokias eventually show wifi with no internet. I thought the issue was only with the nokia 2.2 but maybe this is a more general deco issue if somebody else has the same issue?

My main tp-link deco runs a support provided firmware that allows telnet into it, a tcpdump was run by support, I am now trying to get the deco (at least the main, on my tests I power off the other) to use a specific channel and using 20Mhz in the 2.4Ghz (command to be provided by support), to put it into the same channel and width as the ISP router wifi (channel 6 and 20Mhz), turn ISP wifi off and redo my usual test with the main deco only, see the outcome.

I think @Paqueiros is also Portuguese... can this be something affecting the "Portuguese" deco's?!

@VCL 

Yes I'm also Portuguese, and after reading your post its sounds exacly like my issue, but with diferent smartphone model, so maby the problem is between deco firmware and android software. Did you ever manage to get it solved?

@kevin_z

All advanced configurations have been turned off since the problem first shoewd up, as soon as I can I'll send prints. 

@ivy Ongoing, waiting for another teamviewer session so that support can apply the switch to channel 6 and width 20Mhz on the 24Ghz.

And I also have the deco's as dumb as possible with everything extra disabled, and fixed IP for the nokias. yesterday tried disable the 5Ghz, turn on priority to the nokia, still have the ame issue. One thing I noticed is that while the nokia is "sleeping" (screen off) it is pingable all the time, as soon it wakes and I start doing tests (display a long video using teh youtube app), I notice those ping request timeouts to the nokia 2.2 (android one 9 pie).

I also just got a nokia 4.2 (also android one 9 pie), and this one has no issues and is always pingable.

Now, for @Kevin_Z, the decos run openwrt, I see a lot of people with the exact symptoms we have on their own routers, can this be an openwrt issue? 

@Paqueiros 

The channel and width change to 6 and 20Mhz (kudos to tp-link) made no change to the nokia 2.2 issue, still happening.

I think we tried every single possible change to make the deco as dumb as possible, and as tunable as possible, without digging deeper into specific configurations (like key type, timings, etc., I found a lot of wifi issues as well with openwrt). While I did not test AP mode, I was sure this would not change a thing, as @Paqueiros confirmed. If this was a "general" android 9 issue, I also have a nokia 4.2 with me, that runs also android one 9 (however a complete different CPU inside than the nokia 2.2), that has no wifi issues (and only supports 2.4Ghz as well).