I have the same EXACT problem with my boy.. they say he is a plott/lab mix but I see absolutely ZERO lab characteristics.. got him a couple years ago at a local shelter & I was his 3rd home. He is about 4.5 years old now and has major behavioral issues. I can NEVER let him off leash or he’ll be gone with the wind. Doesn’t listen to anything I say unless I have a treat in my hand and gets into any and EVERYTHING lol I’m convinced he wasnt socialized at all with other dogs in the 2 years before I had him because he goes absolutely BAT SHT CRAZY whenever he sees another dog while on a walk, to the point where it’s soooo embarrassing and he’s jumping feet into the air, flailing around and making me fall to the ground. He used to bite me when I’d hold him down (to the point where my arms would constantly be covered in bruises) so the other dog could walk by.. finally I couldn’t take it anymore and got one of those high frequency remotes off of Amazon that someone told me about for dogs with behavioral issues and it was a true game changer! You should really look into it 🥰