Page with form hangs before rendering complete

I’m not sure if I have one problem here or multiple problems, so I’ll describe some symptoms that may or may not be related.

When I try to view the test page (see link), the first screenful of content is dimmed and a busy spinner appears and never ends. The weird thing is that “below the fold”, i.e. scrolling down, the rendering appears to be complete. I’ve never seen anything like this. The part of the form I want to test, the total field, looks normal but doesn’t work (yet), but that may be because the page isn’t fully loaded.

In case it’s helpful, my environment is WordPress 5.4.2 running the Twenty Ten theme.

The other, possibly unrelated, aspect concerns the formula in the total field. It’s attempting to add the optional fixed membership fee to a variable number (possibly none) of user-filled amounts in a repeater. Here’s my formula:

Annual membership fee+Repeater.GetTotal(‘rnField11’)

After entering this, I clicked the Validate button and got this message:

An error has occurred
SyntaxError: invalid or unexpected token

At first I thought this was my main problem. However, when I downloaded and imported the Repeater-calculations-demo from the Smart Forms Manual and tried the Validate on its formula, I got the same error message! I went on to test the demo in a page, where it loaded normally and worked correctly, despite the reported error.

At this point I’m baffled and would appreciate any help.

The page I need help with: [log in to see the link]