Its all very disappointing, i wanted the 10Gbe LAN downlink to my LAN and with Drayteks superb session based load balancing I was going to feed it with about 1.5Gbe of internet over 2 FTTH/P and a 4G backup.

It shows promise, so I'm sticking with it, but only in my test rack. When there have been a few more firmware upgrades (with corresponding release notes) I'll then put it into live replacing my 3900's where appropriate.

An update to my problem:
I have opened a support case but not making much progress with it yet.
Upgraded to the latest release candidate firmware, had no effect.
Tried the VLAN's as timbelfall suggested but had no effect.

Having the WAN connected causes no problems. Having a direct connected PC to the LAN ports causes no problems. Only when connecting any LAN port to the LAN switch does it die. The problem affects all networking, including the WAN and any direct connected PC. If you disconnect the LAN then the problem still persists suggesting that some system within the appliance has entered an unrecoverable state.

The behaviour is unusual and I think must be a bug that only a firmware update can resolve, unfortunately I may not have time for that and will need to look for a different solution.

Seriously? So the flagship new router in the range basically doesn't work on any of the available firmware versions?

Certainly not an isolated problem by the number of reports here. Surely if you all have the issue it is easy to re-create and Draytek should be able to do so quickly, and thus at least comment on the problem with an indication of potential fix.

How did this one get out of the door with such a basic bug?

My thoughts exactly, it was easy to replicate, I set the thing up on its own so I could see the setup on my 3220, as soon as the wan and/or lan plugged in, it died, or went ultra slow, I did occasionally see max cpu on both processors.
Did this 4 or 5 times before giving up.

An update to my situation.
Have worked through a number of things with support and they only appear to consider it being a broadcast storm bringing down the router, passing the problem back to me and not acknowledging any fault, despite me giving them enough clues that it couldn't be.
Why would it persist after disconnecting from the LAN? I reconfigured it and connected to a different LAN with only a handful of devices and very little traffic and the router crashed as expected.
Still pursuing the broadcast storm theory they asked me to connect it to a switch not connected to the LAN to see if it worked then, which of course it did until I then patched that into the LAN.

I have spent far too long trying to get this to work, I too will be returning the unit.

I'm tempted to try the 3900 which runs different software but as the saying goes - once bitten, twice shy.