Uh... this is weird. You're right, temperature would be the first thing coming to my mind.
I've had my bow for a few years now in a room that gets up to 90, and I recently decided to check its actual draw weight and speed, as I was afraid it could have deteriorated with the temperature, but it had the same draw weight as when I bought it, almost 10 years ago.
Is the bow exposed to direct sunlight? Do you carry it in the trunk of your car when it's hot? Are there hot water pipes running anywhere nearby, or in the wall? Has anyone else access to the bow? (I found a dent in mine after coming back from a trip, I think my old landlady got nosy...). I Wouldn't know what else to think, you shoot heavy arrows and say never dry fired it.