90's with the back on constantly in zero latency, or shooting many frames in a row without pause, would cause higher than usual noise in 1 sec exposures.
I notice this with people who bracket long expsoures. If you do a 30 second, then 15 second, then 8, then 4 seconds, then 2 second exposure, and you don't have any break between the images, then the last image will have noise similar to a 1 minute exposure since at the end of the 2 seconds the sensor will have been on and heating up for 59 seconds worth of exposure.
In reference to the above from Doug Peterson.
I am a Leaf user, but since the Phase IQ backs now use the Dalsa sensor that Leaf uses, a long exposure technique that Yair Shahar taught me to reduce hot pixel noise may be helpful and worth a try.
Try a very short exposure following each long exposure. For example, shoot at 1/500th after a 4 second exposure. Somehow the quick exposure helps to flush out the buildup of hot pixels. It won't completely eliminate them, but it is much better than shooting 8 sec several times in a row, or a series of long exposures brackets.
I live in the desert and over half the year we have temps in the 90's - 110's even at dusk. I do well with my Leaf Aptus, but the thought of upgrading to one of the new backs with the battery contained inside the back is a bit scary. I may be sticking with Aptus for now, as the new backs do get alarmingly hot!
However, I think it's kind of silly to setup up in direct sun at such extreme temperatures as 115F. A simple umbrella to shade your camera and digital back is easy enough to carry and use while shooting or waiting for the light, etc. and also is handy as a wind break during long exposures.