My office tank has been running a little hot lately (82-84+) . The room temp
hovers around 28°C at the moment, so the SAEs are near their max temp?

I did a water change recently and matched the input temp to the existing
tank temp. The next night I saw an SAE lying on the bottom breathing
rapidly. I turned the light off, added extra aeration and (slowly) cooled
the water slightly, but the SAE was gone within an hour. I've been leaving
the lights off and left the added aeration, with no further losses. The tank
temp has dropped to around 80 or less.

I'm more inclined to suspect something funky about the water change, but
could the marginal temps be the primary factor?