Hi again PP
I wouldn’t recommend putting food directly into Vyv’s house, it could attract all manner of unwanted attention. I was going to suggest putting the food out only at night and bringing it back in again in the morning if squirrels were the culprits, but squirrels wouldn’t be interested in chicken cat bics (at least they’re not here!). Other possible culprits could be cats, birds, or rats (I’ve seen the Blackbirds bravely venturing into my cat-proof hog feeding station to steal the hog’s cat bics – even though I put food out specially for them daily!
One guaranteed option (which I use when soft-releasing hedgehogs) to safeguard Vyv’s winter store is to place a rabbit run (or similar) over the house and food - you could cover part of the run with waterproof roof-felt or similar to keep the house and food dry. Once Vyv wakes permanently from hibernation, if you want to keep the set-up in-situ
and let him have the freedom of your whole garden, cut a small gap in the wire mesh of the run and wedge a piece of U-bend pipe (large enough for Vyv to fit through) into the gap - this would permanently prevent cats and birds from entering to steal the food (don't know about rats though - fingers crossed your culprits aren't rats!!).