Problem after Update to WordPress 5.1

Hi,

there seems to be a problem after the recent update of WordPress to version 5.1.

Two people have also mentioned problems after that update in their support requests; what I experienced is that after the update, saving an existing portfolio layout results in deleting all added posts (specific posts layout).

After that, posts can also not be added any more, on one development site it even seemed to crash the frontend site (freezes).
I will try out rolling WP back to version 5.03 for now…

Thanks for any fixes!