You knew the day temps, which are fine, but the night temps are the ones that can cause problems in your case.
Humidity may also be a culprit.
If the night temperatures dropped far below 60 F. Your Psychopsis
Mendenhall got stressed.
These plants don't experience much of a temperature difference throughout the course of a year. They gnerally don't experience drastic day and night temperature differences in the wild either.
Here's a link to a culture sheet for one of the parents of Psychopsis Mendenhall.
Psychopsis papilio Culture