Adobe XD endlessly "Connecting", cannot open documents

This (known) problem has been happening more and more lately. Opening an existing document will very often show a "Connecting" message that never goes away. 

I have rebooted. Mac OS is up to date. Creative Cloud is up to date. Adobe XD is up to date. I have signed in and out of Creative Clould many times. This happens on my local network, or if on a different network. I was able to open documents yesterday and this morning, but in the middle of the day I tried to open another existing document and discovered all documents would show this error. Closing the "working" document then re-opening it resulted in the "Connecting" error. This also happened late last week. I rebooted once, same error. I rebooted a second time, it worked. 

Creating a new document shows an error at the top of the document, "Disconnected from Creative Cloud" "Something went wrong with your connection with Creative Cloud. Work in offline mode until we reconnect you automatically." Again, my Creative Cloud connection is working fine in all apps I've tried, including the "Creative Cloud" app itself, no errors. 

All Adobe apps are working fine, Adobe XD documents are the only problem.

Please help. I have countless hours of downtime due to this problem. I am at wits end.