Hi ZenLuiSL,
As it is not possible to determine the exact cause, you can do the following tests:
1.Does the owner of the queue mailbox have a licence?
--Adding license to the owner of the queue mailbox.
2.Check for duplicate mailboxes with the same email address?
3.Have you set 'Record Creation and Update Rule' on this queue?
--Tried to disabled it for now, until you can check it’s logic in detail.
--Check that the owner of the creation rule connected to the queue has sufficient rights
4.Remove the duplicate email address from the contact.
5.Clarify if you’ve already mitigated the problematic plugin/workflow/process acting on contact creation.
If none of these work, I suggest you create a support ticket for professional assistance following the below procedure.
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