Enketo Web Form failing to load

It's not the number of choices that are the problem. You can confirm that at https://getodk.org/xlsform.

I bet there is some networking issue that is preventing the form from loading. Does a simple one question form work on the server?

Try running commands at Form Loading Error when using Enketo on ODK Central - #4 by yanokwa to check what's happening inside the Enketo container.