If you are able to access your modem system log (radvd is about IPv6 advertisement) and confirm it is power cycling then dont bother looking into LCP echo settings. The router would not fall over and reboot due to this, I am only talking about the keep alive of the PPPoE session from your router.
ISP may be able to reboot your router remotely, I would think, but I’m not certain, not without re-reading the spec. ISP-remote config (so-called TR-069) is something that can enabled or disabled.
> Should I disable it?From the point of view of security you could argue that it is a good idea to disable such things. It also depends on whether or not you trust your isp. If you actually want your isp to be able to reconfigure things, do software updates that kind of thing and do automagic zero-config installations in future then you and they might find it useful. Talk to them if unsure.
So that would be when the data through the modem suddenly increased.Usually by swapping it out and temporarily using a different PSU.