Perhaps you just need to spend a bit more time in his room with him then, rather than waiting for him to come out. It could well also be related to the weather/seasonal changes.
Good boredom buster toys are:
Tunnels and piles of boxes with holes cut in them, for the bunny to explore, chew, hide in, jump on, rearrange. Boxes are my bunnies favourite toys.
A digging box – fill a large box with shredded paper (or soil or sand or any other digging material – paper is just the least messy!), and hide a few pellets or treats in it that he has to dig for.
Fold toilet roll tubes or paper bags with small treats or his bits of his veg portion in it that he has to tear at/open to eat
Willow or apple twigs and tubes
Hide veg/pellets around the room
You could also try teaching him little tricks, like spin, answering to his name, high fiving, standing on hind legs etc, as a way to interact with him and stimulate him a bit more.