I've upgraded EM to 5.2.3 on my local copy of a site that has the events page two levels deep in the menu, e.g. example.com/level0/level1/events. This results in a page not found error. Looking at the rewrite rules with an inspector, I see that the rules are now events/* instead of level0/level1/events/*, and downgrading to EM 126.96.36.199, they return to level0/level1/events/* as expected.
I see that classes/em-permalinks.php now uses the post_name instead of the path, which I'm pretty sure is not what you want here because WP is looking up the page using get_page_by_path(), and that wants the full path to the page. Incidentally, it also means that if there's an attachment with the same slug, the attachment's post will be pulled instead.
Let me know if you need me to provide more detail.
Luckily, I haven't upgraded EM on the live site yet :)