Is it the HOTSPOT that has dropped to 77 degrees? Or the ambient temps?

If it's the ambient temps...I would imagine the room you've moved the rack into is colder, or draftier than the other one.

If it's the hotspot...have you checked the thermometer probe placement? (assuming you use one with a probe) Also, have you checked all the connections between the power cord and the heat tape to make sure nothing came lose in the transport?