I just upgraded my home router and it is fixed

True, no mention of QOS being fixed but I applied this firmware on a router which had a broken QOS page and it's working OK again.

This new firmware for 2865 - 4.4.5.3 - is a piece of garbage!
My main business router has frozen twice since I applied this firmware.
When it freezes - none of the Ethernet ports power up!
The router then becomes inaccessible from the outside.
had to roll back to 4.4.5.2 which has a broken QOS page!
Truly, truly shocking.

Interesting. I've been running 4.4.5.3_RC3 for about a month on my 2865ac and its been the most stable since v4.4.4.x

Might be worth disabling features one by one to see if you can narrow it down and work with Support.

True, 4.4.5.3_RC3 was OK but surely, the final version should be better than any beta (release candidate) one.
Anyway, I am seriously tempted after this whole mess with firmware to burn all the drayteks and roll out something else as this getting rather ridiculous.

I am a bit fed up with this firmware saga so if anyone from Draytek support is reading this - feel free to reach out to me.