Hello everyone,
We definitely have not forgotten about this issue and we have been watching this thread. We hear your feedback. I understand not being able to play custom games can put a damper on holiday plans. 
What we have seen so far is that the error may come and go depending on the time of day, and not all maps are affected equally. Some of the most frequently played maps may be unaffected for example.
I can confirm that our Starcraft team is working on this issue and are working to isolate the root cause, so hopefully it should not be much longer until it’s all cleared up. We will make sure to update this thread once it’s confirmed fixed.