Any ideas why the VPN tunnel has dissapeared? Remotly does store last selected network interface and when it is again available uses it. It should revert to VPN tunnel when it is visible again.
Usually we make such tests with a computer that has ethernet and WiFi available. So on the list of network devices there is "Default, Ethernet and WiFi". If ethernet is default or is selected and we disable it in the device manager (by disabling the physical ethernet card) Remotly will switch to WiFi. But if the last selected by hand device is enabled again in device manager Remotly will switch back to it automatically.