Demos are from the demo farm and straight from the codebase (they all update daily at midnight PST).
You can see more details on the demo farm here: Demo farm and up for grabs demos are back!
Note there are development demos for Ubuntu 16.04, 17.10(php 7.1), 18.04(beta version using php 7.2), Alpine 3.5, Alpine 3.6 (php 7.1), Alpine 3.7 (php 7.1)
I wish I could figure out how to get a Windows demo in there, but haven’t had time to figure that out.
What OS are you seeing your issue in? Also ensure you are not logging php errors to the screen; this is a common reason why things using ajax can error out (since you are breaking the connection by including php messages in the output).