We've just been working on a site where a number of users had the Group Calendar showing their scheduled information as "info restricted".
Looking at their mail preferences, we could see that a mail policy had set their schedule access to allow "everyone" to see their schedule information. This was locked to prevent change. Everything looked OK.
We "back out the policy" and then selected the "Only these people and groups" option. At this point names that had previously been configured appeared.
Removing these names magically corrected the problem and the system began to work.
Hopefully this information is going to save someone a truck load of time.