Emails without bounce notification are not arriving

Dear SAP Community,

in our Marketing Cloud Project we are using SAP Interconnect to send our emails. Unfortunately, we have the following problem:

After executing a campaign, some contacts receive the interaction "Outbound email" and are not returned as soft/hard bounces or as email complaint. Nevertheless, these contacts are notifying us that some of these emails do not arrive in their inboxes.

We have another case of contacts with the interaction "Email complaint" with the description "Dropped-Finished-Previously_bounced: null null" and these emails are not arriving in the spam folder of the contacts. Is this happening because the contact has had a bounce previously and the email is not even being sent?

We have opened an SAP incident to understand this problem better.

In the meantime, does anyone have an idea how we could start solving this?

Best regards

Jose Rangel