Why do VPNs from Rostelecom fail?

Question

VPN

Rostelecom provides a VPN channel through a telephone line. The output is a Zyxel660RT2 modem in network bridge mode. The modem is connected to a switch, and the rest of the computers in the office are connected to it.
Some computers stopped seeing the node on the other side of this VPN. It happened in my absence, the employees say that they "did nothing." I tried disabling antiviruses, firewalls, etc., it did not help. I tried to set up static routing through computers that see the node, it did not help.
Tell me, what could it be?

Answer 1

View switch config. Or the switch is not managed? And restart Zyxel, then call technical support and ask them, for their part, to restart Zyxel too.