I just checked with one of my vampires and it's working okay for me. Dark Meditation restored Vampire Energy. Sleeping in a coffin also restored Vampire Energy. I didn't try hibernating. This Sim has the Sleep of the Undead weakness, so he can only sleep in coffins, but sleeping in a bed should work for vampires who don't have that weakness.
You might try the Sunlight Reversal cocktail if you have someone to make it and enough ingredients. That should make the sunlight restore your Vampire Energy instead of draining it. You learn the recipe at level 11 of the Vampire Lore skill. You'll need 2 Garlic and 1 Plasma Fruit per drink. I recommend growing those in the garden, along with Wolfsbane, unless your vampire lives in Forgotten Hollow. You could also just buy the seed packs but that gets expensive.
You'll need Vampire Lore skill 15 to make the Ultimate Vampire Cure. It takes 10 each of garlic, plasma fruit, and wolfsbane.
Since Vampire Energy is recharging for my vampire, but not for yours, I suspect you have an out-of-date mod or a Sim who's been affected by one. I don't use mods but the normal advice for mod problems is to move your mods folder to the desktop, delete the localthumbcache.package, and then test to see if the problem is fixed.
