If you create a rule that monitors certain activities, it's not possible to subscribe to activities that have some restrictions (tested with Date availability condition). I think users with privileges (manager, teacher) should be able to subscribe to such activities.

Steps to reproduce:

1. Create two forums, A and B, A is open, B is restricted until some date in the future (Restrict access: Date).
2. Create a new rule, Area to monitor: Forum. Other fields are default.
3. Ensure that you can't select a forum B that has a date condition under "Rules you can subscribe to."

The screenshots show where the issue happens.