TP-LINK Archer C60 v2 OpenWrt 19.07.5 Wifi crashing during Whatsapp Call

After anout 30 minutes into the call the Wifi on my smartfone crashes and the call is interrupted.
After reconnecting to the wifi and resuming the call it happens again after a few seconds.

My firmware version is
OpenWrt 19.07.5 r11257-5090152ae3 / LuCI openwrt-19.07 branch git-20.341.57626-51f55b5
I have disabled my 5ghz wifi but the problem still persists.

I am also using luci sqm.