I've been printing in my workshop where the temperature has been 30 - 35C (Australian Summer). I think that these ambient temperatures may have contributed to corner lifting. All I can suggest is that if you are working in an attic, set up a cooling air-conditioner, but be careful about humidity. A small portable unit should do an attic space. If the temperature gets above 25C, try doing ABS prints with the print board at 90C.

Old Man Emu