I have a draytek vigour 2865 running load balancing across 2 lines
1) is BT / Vodafone VDSL2 line - WAN1
2) is 1gbps community fibre line - WAN2

This firmware update to 4459_BT has been a real headache for me.

I have 2 load balanced WAN lines one of is a 'DSL' 68mbps line with vodafone / bt-openreach after much troublehsooting I have now concluded that there is a compatibility issue between the DSL modem compnent of the draytek and the DSL line that exists in the firmware of 4459_BT and vodfaone 68mbps DSL otherwise known as FTTC.
The result of this is the draytek cannot ping the dns server in my case at google 8.8.8.8 ( commonly set) to verify line quality, this then throws it into a tizz an paying no regard to the second WAN link ( which is stable).
This then causes disruption in your internet connectivity. and downtime for 40-90 seconds while it reboots and obtains a new ip address via dhcp for the line. Reboots happen many times daily at random times.

Draytek support have suggested to try the 'varient ' downloads of said firmware these are MDM0, MDM1, MDM2 upto MDM5 all in all we have 7 varients, my draytek used to work perfectly.

Not after this update am now working through the varients with different modem codes

I think i have got stable line back.

I have done 4 things:
1)Read through forum posts of userswith similar issues
2) they mention suspect P5 port & newer firmware instability issues so I have now...
3) downgraded to 4.4.3.2 firmware & unplugged anything connected to P5 port
4) turned of QOS features for few common things eg netflix youtube etc

Broke new ground have gone 36 hours with no restarts so is now a LOT more stable!

Hi
I have major problems with multiple 2865 routers with this 4.4.5.9 and older and newer firmware.
Are you using WCF Web Content Filter feature?
I've noticed that if I have WCF enabled in the firewall rules (so basically using this feature for checking the traffic) - router will reboot at random.
When I disable this WCF in firewall rules, so stop checking the traffic - the router remains stable.

So I got almost to 48 hours but then it done it again 1 second downtime!
however it is a LOT more stable. I will check WCF to see what its doing and update this thread later.

1sec downtime due to reboot is not what I have ever experienced myself with any Draytek routers.
Usually if the 2865 router reboots - it takes 20-30 seconds/pings before it's online again. 2860 were much faster and rebooted within 10 seconds.

How are you checking uptime? via some external tool or are you looking at the dashboard ?

Yes your right, usually it takes at least 30 seconds to restart , this occasion there was no restart, instead was just a 'blip' so then as you can see from my screenshot its been up and stable now for
more than 48 hours, the tool i am using is a continious internet monitor by startrinity (can find it on google) from a PC on LAN this means the 'blip' maybe caused by something else.
WCF is not configured however I do have partially configured DNS & Web content filter profiles but i can revert those back to defaults as not used.