We run a multilingual eZ system with multiple SiteAccesses. The default SiteAccess is "de" (language: ger-DE).
I think there is a content/edit issue while using the page builder. The page builder preview does not automatic matches the language against the SiteAccess.

Everything works fine if I am going to edit content as following:
1. Open content/location view for content
2. Open "Preview" from main menu and select preview SiteAccess manually ("en")
3. Navigate into edit (edit in "eng-GB")
4. Preview shows correct SiteAccess (points to "en")
5. Preview shows correct content because given edit language is registered as allowed language for SiteAccess

But if I am going to edit content as following the preview points to a wrong SiteAccess:
1. Open content/location view for content object
2. Open edit directly via. sidebar navigation NOT through "Main menu -> Preview" (edit in "eng-GB")
3. Change the edit view to page builder through info bar mode switcher
4. Preview points to default SiteAccess OR the last SiteAccess which was selected inside the "Preview" main menu tab (for example "de" with language "ger-DE")
5. Preview shows wrong content because the edit language is not registered as a allowed language for given SiteAccess

From editor perspective this behavior is confusing.
As default the preview have to point to the first SiteAccess the edit language is allowed for and there must be a solution to change between all matching SiteAccesses.