As part of the recent security issue we've been forced to upgrade all our client sites from Page Builder v3 to Page Builder v6.6.2.
That also saw us upgrade each client site to use Joomla v5.4.6 and we're running PHP 8.5.7.
We typically advise our clients to build articles using Page Builder rather than using the Joomla Editor and often the quickest way of them doing that is cloning previous articles that have a similar structure to the one they are writing.
If I open a previous article built originally with PB v3 and click to edit the content in the backend editor it opens fine and allows the article to be edited without any issue. I can then copy that article without a problem.
If however you open an article that has never been edited before in PB v6, click Save as Copy, then go straight to edit with Backend Editor in the cloned article you get the error "Unhandled Runtime Error, TypeError: can't access property "xl", e is undefined".