First off i'm sorry for your loss.
The death could be a number of problems, the answers to the questions already asked would help greatly.
There is a big difference between high humidity in the jungle and high humidity in a tank. Your snake tends to collect more water with high humidity in the tank, and this can cause water blisters. This can be a place for bacteria to enter the body and cause an infection. This is a definate possibility, however the answers to the other questions will help us rule out other things.
But yes, 80-95% is WAY too high humidity. I have coco husk substrate, rewet it about every 8-10 days. As I rewet it the humidity reaches around 90%, then over a period of 8-10 days it drops down in the 60's. This lets my cage, substrate, and snake dry out a little (but not too much> Helps prevent mildew and mold growth, and water blisters.
Again, sorry for your loss.
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-Chris
0.1 Licorice Stick Black Rat
1.0 Black Rat
0.1 Vietnamese Blue Beauty
1.0 Green Tree Python
0.1 Texas Bairds Rat
The educated are the few. The uneducated are the masses.
North American Rat / Corn Snake Care Sheet