WiFi on phone not working after being idle

[VikingGaming]

I have been struggling with an issue on several mobile devices now for a few months without finding a fix that actually works. I am connected to my WiFi on the 5Ghz bandwidth (almost completely free from interference by neighbors) with my Huawei P20 Pro (problem also exists on 2 HTC U11 devices). I am able to access the internet just fine, but if I leave my phone for a while (say, 30 minutes), it will show as connected, but it's then unable to contact the internet, and every app will say that I'm not connected. The only way to solve this is to turn the WiFi on and off again on my phone. I have checked every setting I can think off on all phones affected, but I can't seem to solve it by changing any of those. I am therefore led to believe that it is a configuration error with my router. The problem has persisted through several OS updates on the phones, as well as at least 2 firmware updates on the router.

 

Setup:

Phones: Huawei P20 Pro (Android 8.1) and HTC U11 (Android 7 I think)

Router: Asus RT-N66U, Firmware: 3.0.0.4.380_8120

Band: 5Ghz, Bandwidth: 20/40Mhz, Control Channel: 40

Band 2: 2.4Ghz, Bandwidth: 20Mhz, Control Channel: 11

 

Any suggestions/input would be appreciated.