On your phone uninstall the galaxy wearable app and then reinstall from play store, i had to do it twice but my watch is now fine, hopefully it will work for you.
I did send my watch 46mm back to repair this AOD problem.
In one week the new Watch arrived, (TOP SERVICE COOLBLUE BE) but this new Watch have the same AOD problem.
I discovered the main solution after seaching for ours.
Just set in health app the hartbeat on " NEVER"
Now the AOD is working perfect.
To measure the hartbeat I push manualy.
Hope this is helpfull for all.
I will inform Samsung about this, they will resolve this problem hopely soon with an update.