Hi, sometimes the MB Group Skin just repeats the first value. Mostly it works correctly for that field - so I know it should work, but every now and then the same value is just repeated and only for that one post (the rest will still have no error).
I do not understand why this error is only occasional (and does not occur for all) and even how to fix it. The values save correctly in the MB field.
Can you please share some screenshots of the issue on your site? And the code that you use to create the custom field or screenshot of the field group in the builder.
If the issue only happens sometimes, you can try to deactivate all plugins except Meta Box, MB extensions and switch to a standard theme of WordPress then check this again.