New owner- hiding question

I’m helping my 10 yr old son care for our first boa. We’ve got an 11mo old voice/anery. Humidity is around 65-70, and a hot side of a 6x2x2 at 88. We’ve got many hides, foliage and other clutter since it’s a big enclosure for his current size.

When we first got him he took to the enclosure and several of the hides very well. Was eating and seemed happy and healthy. Last Saturday he disappeared. Cam out Monday to bask and since has been completely gone again. He’s obviously burrowed into his substrate but we can’t find him anywhere. Understand from research that snakes do this. But should we worry about the length he’s been burrowed? He did look a bit dull when he came out to bask so wondering if he’s shedding? Should we not worry that he was due to eat a week ago and let him come out when he’s ready? If we set out a mouse will he scent it and come out?

Any advice is appreciated!