Apple Watch 3 Ultra, Ultra Slow Charging.

I have a brand new (4 weeks old) Apple Watch Ultra 3, updated to latest OS, battery condition 100%. Not faulty cables or adapters (I have several I can switch between). I suddenly started charging slowly, and takes forever to charge (two hours increased it from 20 to 36 %). There are no changes in anything.

This happened from one day to another. I have usually charged it every second evening, and it has usually taken a couple of hours to full charge. I have restarted the watch and turned off battery optimization.

I now have to charge it all night to get it to 100%, and due to that loose sleep/health data for every second night.

Anyone ?