Contacts deleted manually in the source app are intentionally not automatically deleted in the target app.
This ensures that sync.blue® provides even more data security, as contacts remain in other apps even after accidental deletion.
If contacts are deleted in the source, it's technically correct that the originally detected contact count remains for that connection.
However, there are the following ways to achieve this goal:
Instead of deleting a contact completely, replace its data fields with the symbol "-". This way, sync.blue® will overwrite these values in all connected apps.
Manually delete all contacts in the sync target and initiate a full sync in sync.blue® (see sync.blue® Connection - Actions - Full sync). This will re-sync all contacts to the target without the previously manually deleted contacts.