Thanks for the advice!

I removed every bit of the aspen and replaced it with Cypress mulch. I also got ahold of some green moss at the pet store to put under his half log hide. I misted that to get it damp and went ahead and misted the whole terrarium. The humidity reader I have jumped up to 90%. I've been monitoring the humidity levels now for about half an hour, and with the new substrate, the humidifier I have going, and the pillow case covering a good portion of the screen top to keep the heat in, the humidity has been a consistent 90%. I'm sure the number will drop once everything dries (I washed all his toys and did a thorough cleaning before adding the new substrate), but for now, this looks very promising.

Cinna's crashing around like Godzilla again! I'm so happy to see him moving. He's currently exploring every corner of the terrarium even though only the substrate has changed, the goofball.