This is a follow-up to the topic which was closed: https://zentalk.asus.com/en/discussion/51441/battery-drain-when-switching-from-wireless-to-4g
When going from an area with zero cell reception but with WiFi reception, to an area with cell reception but no WiFi, newly started apps will fail to connect to the internet requiring a "Mobile Data" toggle. Similarly, when going in reverse, it requires a toggling of the WiFi.
The phone shows full reception and connectivity but opening a page in Firefox (for example) will fail. Already-opened apps might continue to work and stay connected, but not always.
Same settings as described in the link above: 4G, Wifi6, WiFi calling on.
This issue has been present since day 1 and persists after the latest update.