BUG
I was changing my Custom Field (label description). While the CF was updating I click on advanced. I haven't change anything but the CF was deleted. Also on the fronted I got some error (field ID) was removed.
I have add the field again with the same field ID and now it works.
I'm not able to reproduce the issue on my end. Can you please share a screen record of this issue? Remember to only activate Meta Box and MB extensions when creating the custom field to re-check it.