S8 - wifi disconnects on sleep

[elParaguayo]

I thought I'd post here in case anyone has managed to fix this issue (although, based on my wider searches, I'm not sure anyone has yet).

The issue I'm having is that the wifi disconnects when my phone sleeps (i.e. the screen is off for a number of minutes). This is problematic where I'm downloading data in the background.

I've checked in the Wifi settigns and made sure the "Keep Wi-Fi on during sleep" is set to "Always".

I've turned off smart network switch too.

Is this a bug in the phone or a wider Android issue?

It's quite frustrating for me as there are a number of reasons while having the wi-fi constantly connected is very important for me.

[hrym]

Has this always happened or is it a new problem - and particularly, has it happened after an OS update?   If so, the first port of call is a factory reset (remember to back up your content first, and it's also a good idea to remove the sd card if you have one).   That would be part of any repair process, so you won't have lost anything by giving it a try.

[elParaguayo]

New phone (about 2 weeks now).

Always happened - although I can only really test on my home wifi so far.

An example of this: I've opened an FTP server on the phone to transfer files and switched off the screen. A few minutes later the transfer dies. I then do a scan of devices connected to my home network and the phone is no longer listed. If I switch on the screen and rescan the network the phone appears.

[Tash]

Hi @elParaguayo, please let us know if you experience the same issue when in a different location :smileyhappy:

[elParaguayo]

Yes - same issue on a different wireless network.

[Tash]

@elParaguayo Do you experience the same issues after completing a factory reset as advised by @hrym? Please ensure that you back up your content and data before completing this. 

[elParaguayo]

I haven't tried a factory reset yet but I did want to share some more information.

I was trying to understand what the wifi was doing when the screen was off so I used my laptop to ping the phone's IP address every 5 seconds. With the screen on, ping times were about 50-200ms. As soon as screen goes off, ping times start to vary wildly between 50-1200ms. After 4-5 mins, ping responses stop entirely.

Also, every 15 mins or so, the phone seems to wake for 5 seconds: screen doesn't come on but ping responses start coming back.

[hrym]

FWIW, I've noticed, particularly after the Nougat update (and no factory reset) on an HTC M9 that wifi does tend to disconnect after long periods (such as overnight) and you have to be a bit careful when waking the device up.   It can take a moment to reconnect and streaming, say, the radio, can use mobile data while it's doing it.

Some public wifi, and especially hotels, wants you to sign in again periodically, but that's a different thing.

[elParaguayo]

I may have found a solution.

I had added the relevant app to the list of "ignored apps" in the battery optimisation section. However, I tried using adb to do some debugging over USB and noticed that the UID of the app wasn't in the whitelist (mDeviceIdleWhitelist). I therefore added the app manually (adb shell dumpsys deviceidle whitelist +PACKAGE_NAME) and I've not had the problem since.

I don't know if the problem is therefore Samsung's implementation of the whitelist  or whether it's a problem with the particular app. However, it does seem to be working at the moment.

[Tash]

Thanks for the update @elParaguayo!

Please let us know if you have any other queries in the future and we'll be happy to help.