I have a custom field group: location. One day, it just wasn't visible in the CPT. I thought something might have been corrupted as I tried different things to get it to show up again (flush permalinks, etc), but it didn't work. So I made a duplicate, and then it showed up.
Now, it's super weird again because if I try to put the old custom field into draft, the other one doesn't show up in the CPT and vice versa. I don't know what the heck is going on. I don't need two of these identical field groups, but I'm unable to delete the extra one because the remaining one then no longer shows in the CPT. It's super weird.