My dachshund refuses to pee where it’s supposed to

Hello, I have a one year old dachshund mix. He is pad trained for poop and will go on his pad if he doesn’t go outside. I’m starting to run into a big problem with the pee though. He refuses to pee on the pad, he will randomly pee on the carpet for no damn reason whatsoever it seems. He goes out every 3-4 hours. Actually whats making me write this post is the fact I took him out just like 2.5 hrs ago and I just walked into my room and there’s piss on the floor. He is on a pretty consistent schedule. Meals are at the same times and potty breaks are typically around the same times too. I do know he has separation anxiety so I put a diaper on him before we leave the house, or else there will be small piss spots all over the house but for whatever reason he will still go sometimes when we are home, after we’ve taken him out and while we have him on a schedule. I’m starting to lose it lol