The SCIM user will only be hard deleted from the connected SCIM app when the user is hard deleted in AAD - which happens 30 days after soft-deletion. To be clear though, there isn't a timer on the provisioning side, the trigger for provisioning is for the hard deletion to happen in AAD. Users can also be hard deleted out of the recycle bin sooner than 30 days.
If the user has already been hard deleted out of AAD and is no longer in the recycle bin in AAD, then another reason why you could potentially see a lack of a hard deletion would be if the user was removed from the provisioning scope prior to the hard deletion happening. Examples of this would be the user being unassigned from the application prior to the hard deletion happening (when provisioning uses "Sync assigned users and groups"), or if the user failed to pass any scoping filter groups on the User mappings section at the time of the hard deletion.
If you think none of these cases is accurate, then please open a support case.