Some of this is not a training problem, and treating it like one wastes time your dog may not have. If they are distressed when you leave, if they growl or guard their food, their toys or you, if they are frightened on the lead, or if anything about them changes suddenly at any age, contact your vet the same day. A tip from a website, ours included, is not the answer. If it cannot wait, contact your nearest emergency vet now.
With a Havapoo, watch their back legs, their ears and their eyes. A Havapoo who skips on a back leg, stops jumping on the sofa or sits down on walks may have a sore knee. Head shaking and scratching are often the ears. Bumping into things in the evening, or a cloudy look in the eye, is worth an ophthalmic evaluation (eye exam). A seizure, however short, means calling your vet. A first seizure, one that lasts more than two minutes, or more than one in a day is an emergency: contact your vet now. So is bloat (GDV, a twisted stomach): a swollen, tight belly, retching with nothing coming up, sudden restlessness or drooling. It can happen in any dog, though it is most common in large, deep-chested breeds. From four years, a dog who slows down and gains weight on the same food can have an underactive thyroid.
He'll keep bringing the toy. If he skips on one back leg chasing it, call your vet.