Same thing happened to me. Stayed 58 nights before my end of year trip. End of the year I stayed 5 more nights that ended on the 1st. I called CS and had a discussion about this. I've been diamond since 2012 but since i've never had an issue with needing my last stay. The supervisor I talked to stated simply that management is not allowing for any flexibility and that the best that she could do is send a note to management.
IMO the T&C are a bit vague on when the nights will count towards your stay. They do state the: Qualification for elite status is based on the Member’s activity (Tier-Qualifying Nights stayed or Base Points earned) over the course of a single calendar year, January 1st through December 31st (“Calendar Year”)."
Later this is some language about: "A Member will only receive credit towards elite status for a Tier-Qualifying Night after the Member completes his or her stay and is checked out of the applicable hotel or resort (including for pre-paid reservations)."
I took that to mean that they would only credit you if you check in and check out... (in otherwords no points if you're a no show). However, they could still mean that they credit you your 2017 nights towards 2017 and 2018 nights towards 2018 only after checkout.... to me this language speaks to when you will see your points not which year they will credit towards.
I stayed with Hyatt because of what i perceived to be excellent customer service at the hotels. This is clearly not an example of good customer service. If they are going to deny me status based on a technicality I really have to take my business elsewhere. In my experience Marriott has always been flexible if you are close. With their larger footprint in Europe it should be easier to hit top tier anyway.
To me this almost flippant response of, "I'll send a note to management." Without any promise of followup or discussion pisses me off. Seems like someone who stayed as often as we have at Hyatt should get a better response.