Hello Andrew,
Please update Meta Box, MB extensions to the latest version, then deactivate all other plugins, switch to a standard theme of WordPress and migrate the field group again.
If it does not help, can you please share some screenshots of the issue and export the field group to a JSON file and share it here? I will take a look.
Please read more on the documentation https://docs.metabox.io/extensions/meta-box-builder/#export--import