I read this great answer about how sets work, but I'm seeing behavior I don't understand in this app.
I just installed on a device that has never had the app installed (I think, see bottom) and nothing was restored. Through adb, I tried the command
bmgr restore <package_name> and it said "unable to restore".
So then I did
bmgr list sets and saw that there was only one set available (from a different device). I thought, "well that's got to be the one it's trying to use and failing." But then I ran
bmgr restore <set token> <package_name> and restore worked! And now restore works without the token name either.
If there was only one set to use, why didn't it restore properly? Was there another hidden set? It's possible the app was installed before, but I called
bmgr wipe <package_name> and toggled
bmgr enable true/false to clear any pre-existing data.