i reproduced the problem

power on router
sim card data established
wireguard vpn established
0 wireless client

after some time (less than 30mins), router appeared offline on goodcloud, so i connected to the wireless and login to control panel, it shows
modem connection still active, however VPN became disconnected (shows ‘ABORT’)
because VPN is disconnected, internet became unavailable

in another scenario where the router has wireless clients connected, then the VPN does not disconnect and internet is available continuously

in the logread file, connection lost at around 16:33 time