note to some posters here - OP's post is not about moving rooms but about MHC refusal to upgrade a separately booked reservation with available suite when this reservation is adjacent to another completely separate unupgradable night

along the same lines although not exactly the same - i had a reservation where middle night was not available in a suite but first two and last two were so i asked my concierge to book 3 reservations and apply two SUAs to first and last...
she refused stating pretty much the same reasoning

so i booked two stays via reservations with sua and then booked middle night online. No issues with hotel although as expected we had to change rooms...

perhaps (dysfunctional) hyatt IT system does combine stays and then hotels cant claim reimbursement but it has to be some petty property (eg PH paris) to go after those rare cases and downgrade ppl...