Only reboots have been due to config changes I made otherwise stable.

Have you tried firmware version 3.9.2.5 yet?

There's another thread about 3.9.2.5 being unstable on another Draytek device, constant reboots

kid.a wrote:
There's another thread about 3.9.2.5 being unstable on another Draytek device, constant reboots

If its this thread https://forum.draytek.co.uk/viewtopic.php?f=14&t=23943
you refer to, thats 3.9.5 and is a totally different device.

Ive had 3.9.2.5 since the day it came out on the international site and its been up ever since, apart from missing features the 3910 hasnt rebooted (apart from config/firmware upgrade) or crashed for probably 6 months now.

My apologies, you're right. I wasn't paying attention.

As ever cursed things. I noticed my nas wouldn't work ddns and package centre wasn't working. Since I had been messing around with certificates I thought I'd buggered it up. Later I was on my mac which is running ubuntu and the network although it connected had no internet access. Sounds familiar. Rebooted the router the mac now works. Checked the nas and the package centre now loads. I haven't added ddns back yet but I reckon it will work properly.