I've been grappling with line drops for some time. Gone through several versions and flavours of firmware and have had ISP tinkering.

I've ended up 'putting up with it' for the most part.

But disconnections and line drops are one thing, but what on earth would cause these routers to actually reboot? To my mind, whatever goes on over lan/wan or wifi should not cause the whole device to reboot?

Have I got a faulty router?

I can only speak from my experience with the 2860Vac - no reboots and rock solid.

I have a few firewall rules and schedules configured and SSL VPN - no problems.

Maybe you could try documenting your configuration and then using installing the .rst firmware file to reset the configuration and then add basic connectivity configuration back in and monitor - eventually adding all your configuration back in to see if it is something specific that is causing the issue.

towernet wrote: I've been grappling with line drops for some time. Gone through several versions and flavours of firmware and have had ISP tinkering.

I've ended up 'putting up with it' for the most part.

But disconnections and line drops are one thing, but what on earth would cause these routers to actually reboot? To my mind, whatever goes on over lan/wan or wifi should not cause the whole device to reboot?

Have I got a faulty router?

No, you don't need to put up with it. Mine is now rock solid and is only rebooted by schedule once a week. However, my 2860ac previously would suffer with occasional line drops and eventual reboots even though I am only 25m from the BT cabinet. I fixed my line drops through trial and error with the various versions of modem firmware for the 2860.
Can you post a screen shot of Diagnostics >> DSL Status general tab?