Sorry, but I doubt that was the problem or fix. The Kobo devices do not handle the sort_author in any way. When they process a book into the internal database, only the first creator attribute in the OPF is used and then only the text part. And I have no idea how creating a catalog in calibre could affect the database on the Kobo device.
Most likely the firmware cleaned something up in the database that fixed whatever triggered the first error. Disconnecting the device and restarting it could have triggered something in the firmware to fix it. Or, something else about how you had attached the device caused the problem. Running the Kobo desktop application at the same time as calibre can cause these sort of things.
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