My dog has randomly started testing his boundaries with me after two years and I don’t understand why.

My partner and I got our dog two years ago. I was out of work at the time so I'm the one who initially trained/walked/fed him the majority of the time in the beginning but now my partner does the majority of the walks/food. He is incredibly well trained when there are treats but iffy if theres no big reinforcer. Recently (only when ny partner is not home) he has started winning for no reason non stop, when I try to redirect him to something else he starts running away from me and barking non stop. When I got home from work today I took him out for a small walk, gave him love, and then started working on my computer….thats when it all started. I've tired redirecting by getting him into training mode and by ignoring him but neither option has worked, he keeps running away and/or barking at me. When my partner gets home he's once again cuddly and loving to the both of us.. I don’t know what to do but its incredibly exhausting and frustrating. He never does this when only my partner is home, its a behavior reserved for only me