[ownedbycats]

Thankfully, I'm not getting the same error after updating.

In case this can be used to rule out anything:
Calibre 5.8.1 (x64), Windows 10 Home (19041), Kobo Aura HD (latest firmware).

{
  "SchemaVersion": 0.1,
  "profiles": {
    "Kobo Aura HD": {
      "customColumnOptions": {
        "currentReadingLocationColumn": "#kobobookmark",
        "lastReadColumn": "#lastread",
        "percentReadColumn": "#percentread",
        "ratingColumn": "rating"
      },
      "forDevice": "[removed just to be on the safe side]",
      "profileName": "Kobo Aura HD",
      "storeOptionsStore": {
        "doNotStoreIfReopened": false,
        "promptToStore": false,
        "storeIfMoreRecent": true,
        "storeOnConnect": true
      },
      "updateOptionsStore": {
        "doEarlyFirmwareUpdate": false,
        "doFirmwareUpdateCheck": false,
        "firmwareUpdateCheckLastTime": 0
      }
    }
  },
  "readingPositionChangesStore": {
    "selectBooksInLibrary": true,
    "updeateGoodreadsProgress": false
  }
}