We are currently aware of this and are actively working on a resolution.
In the meantime, you are still able to schedule a session (just not with the specific/intended service type).
Please do so by creating a session from your session list section and then selecting Schedule > Session. When prompted to select a service type please just choose session or any of the existing service types that do appear (even if its not the one you wish). you will be able to switch/edit the service type once we have deployed a resolution.