Caspian,
So sorry... it is very upsetting. Gracious

I believe if it were Chytrid you would have noticed a decline in his activity, eating and overall healthy appearance.
It would not have be a sudden death as described ? Could it have gotten too warm in the enclosure?

My I respectively suggest you were gloves ( vinyl / powerless) during all contact within the interior of your enclosures.... changing the gloves between each enclosure. If gloves are not possible then really good hand-washing with a nail brush between enclosures w/ antibacterial soap and a really good rinse! I believe this to be ' preventive medicine' and should be a standard practice all of the time.

Your caring and attentive. I'm very sorry
Lynn