Currently, survey is not activated, then i can‘t check again. But i think @Joffm use Chrome.

I have enabled preview for non admins.

And I found out one interesting thing :
In an iframe cross-domain ( pilierpublic.com/fr/survey_in_frame ), while the Next button fails in Chrome, it works fine in Firefox & Internet Explorer.

The problem in Chrome (when clicking on Next) shows up in the console as Error 400 :
VM12907 pjax.js:1302 POST lifestooeasy.com/survey/index.php/867832?1561390340470 400
module.exports @ VM12907 pjax.js:1302
loadUrl @ VM12907 pjax.js:286
formAction @ VM12907 pjax.js:751
(anonymous) @ VM12907 pjax.js:769

manual.limesurvey.org/Global_settings#Security
explains further about IFrame embedding :
Theoretically, it is working. However, this function might not work
when it is enabled because it heavily depends on the used web browser
and whether it allows iframes or not.

Which reinforces my belief that one cannot rely on this feature, and thus it is best to avoid iframes (or at the very least put them on the SAME domain).

Just to add something:
There is another thread about iframes here
www.limesurvey.org/forum/can-i-do-this-w...rvey-in-another-site

Chromium Version 73.0.3683.86




But please : try to remove ajax too …