Hi I've just got Draytek 3910 and I'm trying to do a policy route for some pc's on the network.
I've got two isp Virgin and BT
I've put Virgin on Wan5 and BT on Wan 6
Load balance is IP based and I've set the speeds to 350000 download and 36000 upload for Virgin and 76000 and 18000 for BT
So far so good if I plug it into the network it uses Virgin network.
The problem comes when I try to get pc's on say Virgin and another on BT.
So I create a rule using my dryatek 2960 as a guide.
So using a subnet of 255.255.255.255/32 and ip address of the machine involved as the source.The wan is wan 5 However once I Created the rule the subnet disappears to just the ip address and the selection box source changes back to ip range.
So to humour it I just use the IP range.
Check it and the pc is using Virgin and wan5
Add another rule this time for BT on Wan 6 and check again and both pc's now use BT as the default wan.
Whatever I do I can't change this behaviour.
With the draytek I had to create a default route but on 3910 there's no option or if there is it's hidden away.
Reading the manual it suggests I can't route on Lan 1
So I enable Lan 2 set up dhcp on that and try again
Exactly the same as soon as I enter a rule for BT everything switches to Wan 6 and BT
what the hell am I missing ?

You arent missing anything.
At the moment I'm of the opinion the routing screens are a bit buggy.
It does seem to work with basic stuff and I have also noticed things changing when you go back into the rules etc.
Also for me any domain based rules cause it to have a right fit and slow to an almost crash.

Im waiting for next main firmware release, as this version is still way behind their other products eg no USB features.

Like a lot of companies these days this product is at least 6 months too early, but I do love a Draytek and I needed the 10Gbe LAN and NAT throughput.
I can live with it as the only other product within my price range with 10Gbe LAN/NAT throughput was the Unifi Dream Machine Pro, which I have sat here as its a lemon.

So basically it's an expensive brick.

Actually it won't route at all. The diagnoses say it's sent the packet down the right wan but the laptop won't browse the internet at all once you set a route for it.

I dont have any problem sending source IP's or range of source IP's to a different WAN, works fine.
Also port based routing working for me also, at the moment the only problem is domain based routing, which I can live without for now.
If you really not happy then I assume you are still in the window to return? Or have you logged a support ticket with Draytek.
But I sort of agree it was a lot of money for a incomplete product, I can hold out until something better comes along.

Just reading this https://www.draytek.co.uk/support/guides/kb-policy-routing-guide-v2 whether it applies or not is another matter.