Well, the mystery is now solved, but what happened deserves to be narrated.
As you can see, I posted this message in the middle of the night.
Approximately around lunchtime, I logged into flyertalk and was surprised to find a PM in my inbox from a Swiss representative.
The message actually came from an Online Marketing Manager (as I later understood from the email signature), who explained that he had read my post and offered to look into this matter. He provided his corporate email address and asked to send my PNR.
I provided all the relevant information and, two hours later, I received an email with an explanation:
Dear (XXX),
thank you for contacting me so promptly. We checked the history of the booking and it seems, that while the seat assignments were done by the call center agent, the reservation was cancelled by mistake. This was immediately taken up by the agent and the reservation was re-validated and is confirmed in our reservations system. Unfortunately, it was showing up as cancelled when you looked up the booking on swiss.com, probably right after you had talked to the reservations center. Your seat assignment currently shows seats (XX) on the outbound flight to (XXX) and (XX) on the inbound flights back to (XXX) and all flights are confirmed.
Please accept our apologies for this inconvenience. I wish you a pleasant flight to and from (XXX) and hope, that you will use swiss.com again for further bookings.
Best regards,
(XXX)
The Swiss representative is now trying to find out from the technical team why the booking still shows as cancelled, even if it was reinstated as confirmed.
I am nothing short of impressed. I was certainly not expecting such a prompt (and unsolicited!) intervention. I personally feel as a valued client and am now definitely inclined to forget about the inconvenience. Moreover, this is a clear and positive sign that the Airline is gathering feedback from the customers.
For those of you who might be curious, I can report that this Swiss representative does not post here on flyertalk, but mentioned that he is a regular lurker (the profile from which I got the PM was registered several years ago, but has no posting history).
Thumbs up for Swiss!