Dear community a MT sitting behind 2 WAN addresses, when initially connected to the router (please see attached diagram) establishes L2TP/IPsec connection.

However, at random times (could be 5 minutes/1 hour etc.) the connection is lost and although MT2 IP/cloud continues seeing router’s WAN address 90.91.91.1 AND IP/Ipsec/Policies on the CHR server side sees that same address, the link will not establish. As this is a setup at a friend’s house (ISP's modem and up to the router), can you please share ideas why this is happening? I haven’t checked logs on friend’s router/modem but I don’t think either WAN addresses change when the connection is dropped between MT2 and CHR.