Have you cleaned out his house or removed his nest recently? Sometimes they abandon a house or nest if all their scent is removed. His toilet probably still smells familiar!
If the house is a bit small or not dark enough inside they sometimes abandon it too. A shoebox makes a good dark house/hide. I reckon if you made a shoe box house (cut the bottom of the box out, leave the lid as a lift-off roof and cut a door in the front), put some food or a couple of treats inside it and a bendy tunnel over the doorway so it's dark inside, he'll probably build a nest in there
If it's big enough he might move his toilet corner in there as well (mine has always done this when he's in a large house - he has his nest at one end and a wee corner at the other end). If he does this you can move the potty inside the house. Then use the lift-off lid to check his potty without his nest falling apart. They get very upset about their nests being removed - it's their number one most important thing really. So if it gets wee'd in its best to always leave a bit of the original nest behind so it smells familiar. then put a big pile of torn up strips of plain white toilet paper in a big pile somewhere in the cage and your hammy can take some to rebuild the nest. The pile tends to go down slowly but one day you notice a lot has gone.
Spot cleaning every day is maybe a bit too much. I empty the potty about every 5 days and I never take Charlie's nest out if it's dry.
They can get into an itch scratch cycle with cleaning - the more you clean the more they pee on things to keep scent marking them and deter predators. If you remove the hoard they sometimes start hoarding in their potty so the smell deters predators!
I found Erin's Hamster's cage cleaning tips videos really helped me and it works well for our hammy.
https://www.youtube.com/watch?v=5jVnEjrXbww