The only difference I can see between my code for this plugin and for another plugin I made that does work, is that the one that's not working is using groups...
Could you please try to deactivate all plugins except Meta Box and MB extensions, clear the cache then check the issue again? If it still happens, please take a screen record with Loom, share the link and the code which shows value to the frontend in your next post, I will take a look and give a quick response.
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