Javascript doesn't work when Next JS runs inside iframe in Storyblok CMS

[JonCognioDigital]

Bug report

Describe the bug

When I run my site (Next JS 9.4.4) inside the Storyblok content editor (which places it inside an iframe) then no Javascript is run on the site and as such the screen stays blank because of a fix added to a recent Next release to hide the FOUC.

I think javascript execution stops because of the following error:

Error was not caught DOMException: Failed to read the 'localStorage' property from 'Window': Access is denied for this document.
    at initializeBuildWatcher (http://localhost:3000/_next/static/runtime/main.js?ts=1591116741992:11757:38)
    at http://localhost:3000/_next/static/runtime/main.js?ts=1591116741992:13020:40
(anonymous) @ next-dev.js:48
Promise.catch (async)
(anonymous) @ next-dev.js:30
./node_modules/next/dist/client/next-dev.js @ next-dev.js:30
__webpack_require__ @ bootstrap:797
checkDeferredModules @ bootstrap:44
webpackJsonpCallback @ bootstrap:31
(anonymous) @ main.js?ts=1591116741992:1

To Reproduce

It is not possible to reproduce the problem without logging into a private Storyblok account to see it.

System information

• OS: [Windows]
• Browser [chrome]
• Version of Next.js: [9.4.4]

Additional context

Add any other context about the problem here.

[dohomi]

possibly related to #11356 (comment)

[JonCognioDigital]

@Timer - I see the "needs investigation" tag has been added to this ticket. If I can do anything to help then please let me know. I'd be happy to give somebody with a Vercel email address access to the CMS.

[JonCognioDigital]

A little more info, this only seems to happen on localhost. I published to an Azure url today and it doesn't seem to happen. Very odd.

[dohomi]

@jon64digital I have this issue deployed to Vercel as well as on localhost