Thanks again for your help today, Ray. Most files are updating correctly for me, but there's one file that's giving me this alert when I double-click the legacy insert behavior:
RangeError: invalid array length
When I click OK, the alert goes away and the Insert Record window is left completely blank, with just an X box in the upper-right (screenshot attached). I'm also attaching the file in question along with the associated Universal Email file. The only thing I can think that's inherently different about this page from the others is that this form has no file upload field. Otherwise, they're doing more or less the same thing: capturing data and sending an email. Any thoughts?