can you post your configs... i'm not sure I completely understand how you have this device setup. Mainly just the bridge and ppp submenus.
It could be that the MAC address of the bridge is changing due to an interface going up/down, which could also explain why all PPPoE connections are lost. If the bridge's MAC is tied to the PPPoE server and it changes then all PPPoE connections just lost the host they were trying to reach to establish/maintain the tunnel.
In this case I'd set the bridge's MAC address to a static MAC so its not based off of what interfaces are active in the bridge.
Either way you should not lose the connection to the device (enabling RSTP or setting a static/admin MAC). From what I understand you're connecting from the WAN side of the device which is a Public IP of some sort. So you should always be able to connect to that...but if something doesn't go as planned be prepared to take that long drive.