This is bug related to cloning, the forum has multiple entries and the latest version is completely usable currently. Please revert back to 5.9.11 if you can, it works.
This issue has been since multiple days and to my knowledge no response from the team. This is bad for the product, which is a shame. metabox has been our go to plugin for ~200 projects but now I'm reverting all of them back and lots of problems with broken content due to this bug. If this was tested before release none of this would have happened. Perhaps the team has changed?