Hi Gregory,
Thanks for sharing your experience with us.
Based on your description, the error message happens when you click Edit all when editing properties of a document.
Did you contact the user who is mentioned in the error message to check if he/she has checked out or locked for editing the file?
Did you clear the cache of the browser and check the outcome in different browsers?
Besides, please check if you can edit properties of the document via click ellipsis next the document>More>Properties>Edit all.
If the issue remains, we'd like to confirm the following information for troubleshooting:
1.Does the issue happen to a specific document or all document in the document library?
2.For the other users who have access to the document, can they edit properties of the document?
3.Does the issue happen in this specific document library or all libraries in the site?
Regards,
Tina