"This is a non-secure form." when performing actions on JSS (9.93)

[pcrandom]

This just started happening yesterday and seems to only be with Safari (the two systems I tried were 10.0.3, one on OS X 10.10 Yosemite, one on OS X 10.11 El Capitan). When I try to edit or save (policies, scripts, etc.) on the JSS, I get a warning:

This is a non-secure form. This form will be sent in a way that is not secure. Are you sure you want to send it?

If I click Send, the page tries to load about:blank rather than resend the form. Anyone else seeing this? It's very intermittent and didn't start happening until a day or two ago.

It does not appear to be happening with Chrome (55 or 56).

[brodjieski]

I just started seeing this behavior, did you ever get a resolution?

[gda]

Same here. I'm using Safari 10.1.2 on macOS 10.12.6. It happens when I try to create or update a script item. It works well in Chrome.