Hello,
After our communication over email, it seems like this is caused by another plugin (password strength meter) that causes a JavaScript error. This interferes with the JS code for the UIs.
In the upcoming wallets6 plugin the JS code is isolated from other code and therefore this kind of problem will be far less likely.
But for now, any JavaScript errors on your site will cause the UIs to not load.
Try disabling the offending plugin to see if the error goes away. Let me know if the problem persists.
with regards