Why isn't my phone getting any notifications when connected to wifi?

As of last Friday evening, my Galaxy S8 started having problems with notifications when it's connected to wifi. Until yesterday, it wouldn't push any notifications for any app unless I specifically opened the app. For example if I was looking at WhatsApp, I wouldn't get any Facebook messages. As of now, that only happens if my screen is turned off. For example, I go to WhatsApp web, and it tries to load. While the screen is off, it is stuck at almost the end of the loading bar. As soon as I wake my screen up without even unlocking, the loading bar completes and the interface loads. This happens with apps including but not limited to Whatsapp, Facebook Messenger, Signal, Facebook, Gmail, and Google Play Store. For example, while updating apps on Play Store, turning off the screen causes updating to stop and play store to give connectivity error messages. There isn't any problem if I am connected to mobile data.

Things I did in vain to resolve this issue:

Restart phone
Turn phone off and start again
Reset network settings
Turn off smart network switch
Turn off enhanced LTE settings
Set WhatsApp notification priority to on
Update WhatsApp
Turn off power monitor in battery settings altogether
Reset app preferences
Turn airplane mode on and off
Set time to wrong time, kill all apps, and change the time back to automatic
Turn off nearby device scanning

Current relevant settings:

Apps > Special Access > Optimize battery usage > All mentioned apps are off
Battery > Power monitor > Unmonitored Apps > Facebook, Messenger, Signal, Whatsapp --- Gmail and Play Store cannot be added
Battery > Power monitor > Always sleeping apps > 0 apps
Battery > Power monitor > Sleeping apps > None of the mentioned apps

Make sure your device is not on any power saving mode. Also, make sure you select "keep wifi always on".

I'm sorry you're experiencing this issue, OP! Would you consider a factory reset (once all of your important data is backed up)?

Originally Posted by tuscanybay

Make sure your device is not on any power saving mode. Also, make sure you select "keep wifi always on".

Sorry Tuscanybay, I was very tired of trying to find a solution this problem while I was writing this question. I had already made sure that power saving was turned off and keep wifi always on was set properly.

Originally Posted by Morty2264

I'm sorry you're experiencing this issue, OP! Would you consider a factory reset (once all of your important data is backed up)?

My main point of posting this here was so that I could find a solution without doing a factory reset, but oh well! I am usually not against factory resetting, but as far as I could find out on Google (there is almost no issue exactly same as mine), doing a factory reset didn't solve a lot of the similar issues.

Originally Posted by Morty2264

I'm sorry you're experiencing this issue, OP! Would you consider a factory reset (once all of your important data is backed up)?

I just completed the factory reset. The issue still persists, i.e. if connected to wifi, any data connection terminates as soon as the screen goes black; no problem if on LTE. Are there any other suggestions you got?

Originally Posted by Morty2264

I'm sorry you're experiencing this issue, OP! Would you consider a factory reset (once all of your important data is backed up)?

I just completed the factory reset. The issue still persists, i.e. if connected to wifi, any data connection terminates as soon as the screen goes black; no problem if on LTE. Are there any other suggestions you got?

Hello OP, I am facing the same issue as you and it started around a week ago. Have you been able to fix the problem?

Can you rule out it being a router issue or AP device?

Hello, the issue was solved by wiping the cache of the system. Would you try it?