If Banktivity is crashing when opening during the update/sync process you may need to delete your existing sync settings and set up syncing again. You should be able to open folder where your Banktivity Document (data) file is saved (Documents folder is the default save location). Press and Hold the Option key only as you double-click on your Document (data) file and keep the Option key pressed until Banktivity opens – this should open Banktivity without attempting to sync. Once Banktivity opens, go to Banktivity> Preferences and uncheck the checkbox beside “Automatically update documents”.
Next, go to View> Show Sync Settings and click “Troubleshoot Cloud Sync” followed by clicking on the text that says “Click here to stop syncing this document”. Then you should see a button labeled “Set Up Syncing” in Sync Settings, click “Set Up Syncing” to set up Cloud Sync again.
After setting up Cloud Sync again, go to Banktivity> Preferences and check the checkbox beside “Automatically update documents”.