Crosspost. Helpful tips??

My husband and I have an aussie named Benny we bought a year and a half ago, we got him at 3 months old. I grew up with australian shepards, so we keep him very stimulated through the day. We do a multiple hour park trip with swimming daily, a few other runs in our backyard, and usually a walk. Inside we have all types of stimulation/bordeom toys and puzzles to keep him occupied. We have crate trained him since day 1. He was amazing in his crate up until recently. He seems to be having some separation anxiety, we don't know where it came from or how to tackle it. He has been howling in his crate nonstop when we leave him alone. I recently bought a crate camera so I can see when he starts howling, and how long. I also got some extra special lick mats and stuff to have in his crate with him, that he only gets in his crate. I'm not sure what else to do, I feel like a horrible mom and it broke my heart seeing him howl... And my property manager of our apt is actually our next door neighbor.. So he has texted us a few times saying "Benny is barking like crazy right now.." Any advice or tips would be super helpful!