So tonight I decided to try and see if I could tempt him out - but couldn't find him

. Took the house roof off and he wasn't in there - and it still didn't look lived in or disturbed. So I lifted the large ceramic hide out - nothing disturbed under their either. I had been thinking about removing that after watching him on the videos. Because there just isn't any floor space to run around in and he's a big hamster - apart from that he doesn't seem interested in it and it blocks the view of the camera as well. As it happened one of the legs fell off it when I lifted it up, so I decided to leave it out. I think it looks better now - some other things are more accessible.
So I thought he must be back over at the other end under the cork log or the lower shelf - lifted the log out - nothing but clean substrate under and behind it. So I put that back. Lifted up the lower platform - nothing but clean substrate. No sign of any tunnels or burrow entrances anywhere in the cage.
So thought - he must be underground somewhere, but curious I can't see a burrow hole anywhere.
After I went to bed tonight I waited a while and watched via the nightcam on my phone. Saw him out in the cage next to the door so decided to go down and offer him the tube. By the time I got downstairs he was nowhere to be seen so clearly just the sound of me coming downstairs made him hide.
I lifted the house roof off again and he was inside it. Hurray I've finally seen him. Talked to him and he ignored me completely. Offered him the tube and he quickly climbed over the edge of the house at the back and disappeared. Oh dear - he doesn't like me any more.
I thought - well he must be just sitting on the substrate in the gap between the house and the back of the cage as there's nothing else there. So I walked round the side of the cage to look and talk to him - and he wasn't there! When I looked closely there is a tunnel entrance right in the back corner in the gap between the house and the back of the cage. So he has a burrow down there, under the house maybe. Very inaccessible!
So it definitely looks like taming has regressed! It's clear he wants to come out of the cage watching the nightcam videos but isn't responding to me any more. Either in a huge huff at the change, or just forgotten who I am after two weeks!
I'll give it a bit more time.