I have a similar if not exactly the same problem and it started a bit over a week ago.
Every 2 days in the morning the remote access stops working. And I have to reboot my Router Modem to temporarily fix it. But my router modem is set to exposed host. No Firewall, no NAT, nothing. ALL traffic is forwarded to my actual home network router. And my public IP is fixed. So it makes no sense to me.
External access worked for the last 2 years without issues and this just started. There was no update on any device in the few weeks before it started.
