I deleted some contacts and they aren’t deleted in the other app

That’s because we don't sync deletions - a safety measure on our end to avoid PieSync end-users from being able to wipe out (parts of) their databases completely, cross-connections/in multiple apps, when a manual error is made for example.

We do have the syncing deletions feature​ in some of our integrations. This tags the delete from app A in app B, we will never automate hard-deletes but this way you can check the 'trash' segment in app B and hard-delete manually after reviewing. However, this feature is only available when we are able to detect deletions in app A + are able to create a new trash segment in app B at the same time:

There are a few exceptions but since we can add a tag in most CRM's we support and Google Contacts is one of the only apps that allows us to detect deletions, mostly Google/CRM syncs will have this feature available (one-way, Google Deletes to CRM).