Thanks.

I will have to log a call with Draytek.

For me it can only be a problem with the 2860 as the 2850Vn worked fine and so does the BT Homehub 4.

Very disappointed though - I expected a lot from this router.

I have recently purchased the 2860n+, last week in fact, and once I found the settings for connecting with Sky Fibre, I now have a stable connection. My 2860n+ has replaced 3 items now, my BT Openreach modem, my Sky SR101 router and my old Draytek 2830n+. System up time is showing 157 hours and if it helps any with your problem my firmware version was the one the router was already installed with and shows 3.7.3.2 build date Nov 4th 2013 15:20:24. DSL Version 05-04-08-00-00-06.

So I had exactly the same problem with a 2830 and a 2860 and it had the strangest cause: an app on my home NAS.

Setup:
ADSL WAN 1: Plusnet
ADSL WAN 2: BT business on BusinessHub2

Symptom:
Rebooting every 5 minutes, sometimes 20 minutes, sometimes 3. 24/7.

Steps taken:
Switching off WAN2 -> keeps crashing.
Switching off Plusnet WAN1 _> stabilised things (not one reboot in 24 hours).
Switched from Plusnet on WAN1 to WAN2, BT from WAN2 to WAN1 ->Crashing returned.
Switching off BT WAN1 -> stabilised things (not one reboot in 24 hours).
Decide the 2830 is broken and order a 2860
2860 does EXACTLY the same thing!!!!

So its not the ADSL, not the router, not the BusinessHub.

*coincidentally* decide to turn off my home server (Synology).... Internet stays up!
Turn Synology back on -> crashing returns
Block all ports in/outbound except 443 on Synology -> Crashing stops
Open ports one-by-one until crashes resume.

Turned out it was PlexMediaServer (0.9.8.18.290) downloaded from Plex.
Uninstall PlexMediaServer 0.9.8.18.290 -> crashing stops. Stable for 24 hours
Install Synology's Plex 0.9.7.28.33 -> Stable for 24 hours.

Now stable for over 350 hours. Weird Weird Weird. Can't explain why.

Hope this helps.

TGERIGHTY - you sir/madam are a genius and I sincerely thank you for investigating this and getting to the bottom of it. Draytek support - please read and understand TGERIGHTY's post above. Two separate people have confirmed this is the case so I ask you research it and do something about it. It is not PLEX or the Synology NAS that causes this - it is your routers. PLEX runs just fine on the Synology NAS with other routers.

Anyway I have disabled PLEX and the VDSL2 connection on the 2860N+ is solid and stable. TGERIGHTY - thanks once again.

By the way, the speed issue I had was/is nothing to do with the router. It is a BT fault and they are apparently coming out to resolve on Wednesday.

Mike - if you downgrade the Plex to an older version you can keep it running. You can get older versions from here:
http://download.synology.com/download/spk/Plex%20Media%20Server/

Brilliant - thanks.