Well as a test you can enable SB and ABE for a while and test to see what you find out. Then disable SB and ABE afterwards.
We don't know what QC does and will do. You could attempt to contact QC directly to see if they have any information regarding this particular problem and see if they can give you any help.
The more they know the more they are apt to do something. We need to be proactive in helping D-Link and QC in any final problems so that they can correct them before any and all development stops and D-Link moves on to other things. I know that QC should be supporting Sb updates till 2017 from what is displayed on the router. After that, I don't know what will happen. Over all, I agree that it's not been a great ride for everyone, including D-Link. We all had high hopes for a great follow on to the 4500, and everyone already knows, the 5500 may not not quite lived up to expectations on certain levels. It's been a crazy ride.