This appears to be due to a bug in how migration is handled by macOS.

Please try and download the app again from this link and see if this fixes it for you. It may take a few moments to convert the database, but should not take more than 1 minute. If it takes longer, please proceed to the next step below:

https://www.busymac.com/download/BusyContacts.zip

In case re-installing the app does not help, it seems the database has become corrupt during migration and needs a manual reset, like so:

Open Finder, select "Go" from the top menu and then "Go to Folder", and paste the following in the dialog box as-is:

~/Library/Containers/com.busymac.busycontacts/Data/Library/Application Support/BusyContacts

In the window that appears, delete these files: BusyContacts.bsql, BusyContacts.bsql-wal, BusyContacts.bsql-shm

1. Launch BusyContacts again

2. You will have to re-connect to your accounts under BusyContacts > Preferences > Accounts. You can also restore from a previous backup if you had On My Mac contacts (see point 4 below)

Note: If syncing with iCloud, you will have to re-enter your iCloud app-specific password for BusyContacts. If you have forgotten your iCloud app-specific password, you can create a new one and use the new app-specific password instead. You can learn more about creating an app-specific password here:

https://support.busymac.com/help/71150-icloud-two-factor-authentication-and-app-specific-passwords

If you had local "On My Mac" contacts and you wish to recover them, you may restore them from one of the BusyContacts backups that are automatically created each day. To do so, select File > Restore from Backup, and select one of the recent backups from the list and select the local "On My Mac" contacts you wish to restore. You should not restore the iCloud, Google or Exchange contacts, as those will be re-synced automatically in step 3.

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