Keep us posted. I presume your unit needs to be RMAd.
Just got an accepted RMA-notification a few minutes ago, with a note:
"We are pleased to confirm we shall shortly be despatching your replacement product to you at the customer address shown below."
And
"The prepaid return label and instructions for returning the product will be sent to the email address registered to your customer number."
So, this was quick and it seems that I will be able to use this one until the new arrives. And then send this one back.
Well, that's excellent 
P.S. Just got notification from UPS, packet should be delivered tomorrow...
Interesting, I have the same issue with QoS setting being impossible to set. Opening in HTTPS, get a 'Router not found' when attempting to save. Restarting box does not help. Using HTTP then I can 'save' the setting but when the page refresh it is still OFF. Same rebooting DIR890L does not resolve the issue. Wish I could use this functionality to ensure 2 of my high priority but low bandwidth required get ahead of anything gobling everything.
Then there's the issue of QuickVPN that just want to use 192.168.100.2 instead of allocating an IP that is actually within the range of what the DHCP server is set for. Because you know if I VPN to my network under that IP, I get nowhere.
Then there's the issue with 'The maximum number of permitted DHCP reservations has been exceeded.' that even if you go back to other devices and deassign IP reservation, let say even up to 10. The box still refuse to reserve anymore. Reboot don't fix that either, only fix is a full blown reset.
The DIR890L has good performance but the configuration are sub-par, are wonky under HTTPS constantly timing out, or giving router not found. HTTP works a bit better but still get time out when you take too long to make you setting you hit SAVE and get to the login page.
I never been able to run QoS, can I also get an RMA setup?
DIR-890L HW:A2 FW:1.20
Zak