This has been reported before, without response.
If a user receives an invite from external Outlook calendar, and it has an attachment (of any type), then Notes allows to open the invite, but immediately reports the error “One or more of the source document’s attachment are missing. Run Fixup to delete the document in the source database.” If you click OK and return to the inbox, then you can’t open the document again - it reports “Document has been deleted.”
I’m pretty sure this is a local Server or Network (?anti-virus or firewall) environment issue, because it doesn’t happen for me in a different organization.
Can anyone suggest anything please.