importing [...] runs without checking if data is empty:
update_post_meta($id, "wpspin_show_showurl", $show['ShowUrl']);
So when I edit the show for the first time in metaBoxSave, it will get the metadata and the assumption made was the empty string means it doesn't exist, which in this case it actually exists but with an empty string. So then it tries to add_post_meta, but fails since unique is enforced(which is the right thing to do). So the metadata doesn't update.
A fix is not to do update_post_meta when importing on editable metadata fields that are empty. Or, right after doing add_post_meta, check if it failed. If it did then it already exists, so then do update_post_meta.
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