I keep him on aspen substrate, his humid hide is this: https://www.amazon.com/Zilla-Decor-R...57792949&psc=1 which I believe is made of resin, I put sphagnum moss inside it. His main substrate is definitely not wet, I keep the moss damp to provide higher humidity, I just replaced it however and it was pretty dry having needed to be replaced so even that doesn’t seem like it would be wet enough to be the cause. Maybe the moss had some dye added?