If you have either a brand new document or a newly edited one that it is in an unsaved state AND you have just entered a value in a metadata field AND you leave the cursor blinking in that field - when the autosave interval passes and the doc is saved, the metadata field is cleared.*
In my case I was adding the metadata via a Keyboard Maestro macro so it took me a while to figure out why I was having missing data here and there. The fix was pretty simple just hit Return or change the focus away from the newly edited metadata field before the autosave interval passes.
But if possible, it might not be a terrible idea to have Scriv automatically close any open metadata fields before saving.
* other variations that have turned up while testing:
- if you've changed the document and changed the value of the metadata, the metadata value reverts back to what it was originally on save.
- as above, but hitting CMD+S to save, rather than waiting for the autosave