Sounds good. Try switching to 100% cypress mulch as your substrate and leave him on that for 1 week before trying to feed him again. Keep us posted. Good luck.
I know cypress is good for humidity, but I don't see it being a recommendation to fix a feeding issue.
How often do you deep clean the tank? Mine seems to go off food when she decides it is not perfectly clean. And if I don't deep clean after a shed.
0.1 Lesser Pastel
1.0 Black Spooky Kitty 0.1 Faye Tiny Kitty
?.? Feral Cat Colony
And more on the way always....