Hi - this began occurring with me on Google drive today. iOS13.4.1, both on an iPhone 8+ and on a 7 - Codebook 4.0.14 (870). The process gets to about 56% (18/19 files), then appears to stall. Progress bar closes, and the error pops up (“codebook-changesets-569.db” couldn’t be removed. The file doesn’t exist.). The database appears intact on the phone, but is not updated. The same happens when trying to update the database on my laptop (W10 - Codebook v 18.104.22.168) with the exception that there is no error message, and it goes to 75%before the progress dialog snaps closed - there is no propagation of updates to the target machine. I was able to use WiFi sync from my main machine to the two iPhones, and then from one of the iPhones to the laptop - went without a hitch. Still not able to use sync to Google drive even after manually syncing with WiFi, and re-syncing to Google Drive.
Per triage, I tried restarting the iPhone 8+, and I performed an integrity check on the main machine’s database. Neither affected action this issue.
Per your advice to maneson.us, I will also include this in an email to support. However, also putting it in the forum helps others - like me - find the issue if they’re experiencing it, and is also the best place for you to publish advice or solution for the self-motivated… Like they say: you can’t manage a secret!