I had this same issue with Realm works and I fixed the issue by going to the %Appdata% folder for realm works and deleting the main.realm file. After that I logged back into Realm works and it downloaded my realms from the cloud.
This approached worked for all three computers that I was getting Error 301. Unfortunately, if you had made any changed to your Realm after it was successful synced with the cloud, you will need to enter that information again.
-Car
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