There's gotta be something less common about your installs that is triggering this instability. Have you raised a ticket with support?

I agree things have gone downhill with the 4.4.x release family onwards. More bugs, more issues and delayed updates.

Personally, my 2865ac has been stable throughout the 4.4.5.x releases though.

Hi have been in touch with Draytek support about my router 2865 which has been having major issues since April this year.
The major issue was that the router would at random not enable certain LAN ports at all.
I would say that the support had no clue what was going on. Not helpful at all. In total, very bad experience.

I too am wondering what it is that makes some configurations appear less stable.
I wonder what needs to be configured to trigger instability?

Found something that might be of significance.
My wife has been away for the last week, so I have had been able to play with the 4.4.5.8 firmware. The key part to this is that my wife's PC is in the same room as the router and therefore connected directly to it for ease of cabling, all other systems are connected via a network switch to port 1. The significance will become apparent I hope.
The day she went away I updated the draytek to remove any trace of inter-lan routing, and the one VLAN config was cleared via the web GUI - even though VLAN (and hence inter-lan routing) was disabled, there was some configurations still set from past requirements. I then updated to 4.4.5.8 firmware and found this remained stable all week, something it had never done before.
During that week I plugged my backup server (an identical HP ML110 to the system my wife uses as a desktop PC) directly to port 3 of the draytek (wife's PC is in port 5). This was left turned on for at least 2 days as I needed to do some work on it remotely. The draytek remained stable even with 4.4.5.8 and this PC directly connected to the draytek. I therefore assumed that it must be those configs on the draytek I had changed, but...
Wife returned home today, and within 2 hours of her turning on her PC, the router crashed ! Highly suspicious I thought, but might be coincidental.
Upon investigation, the ONLY difference (apart from what physical port it's connected to) between the two absolutely identical PCs used with 4.4.5.8 directly connected to the draytek was that my wife's PC had hardware flow control enabled, the "server" had it disabled. I have just disabled flow control on the wife's "errant" PC and we shall see what happens.
So it's either having a device with flow control turned on directly connected to the draytek that kills the router with 4.4.5.8, or there is something wrong with port 5. But as this ONLY happens with firmware later than 4.4.5.2 (so it seems), I assume port 5 is fine as I hadn't changed anything on the wife's PC before (it has clearly had hardware flow control enabled for a long time prior without any issue).
I will keep you posted if this seems to solve the issue.

But my question to  Geroi is, do you have any devices physically connected to the draytek ports that have hardware flow control enabled? Might be worth checking, disbaling any that have it enabled, and testing 4.4.5.8 again.

My 2865 with firmware v4.4.5.8_BT has been running for over 14 days with no issues.

I have three VLANs configured but no routing between them.
Occasionally do I use the physical ports but always with auto settings.

It is worth noting that the initial setup of my 2865 router was with v4.4.5.3 'factory reset' version so that there were no 'legacy' configuration settings carried forward.

My LG ethernet connected TV now keeps connecting/disconnecting since upgrading to this firmware. I know it's a known issue, but it never happened on the old firmware.