We have a Hybrid Exchange (2010) setup with Office 365. Personal calendar integration is working fine for accounts that have mailbox in Office 365, but it's not working for a user with mailbox on-prem. Though I can see free/busy information for on-prem user in booking calendar. But it does not prevent customers to book conflicting meetings.
When I try adding on-prem user as staff it timeouts and throws an error. But the user is actually added after some time.
Is calendar integration with hybrid exchange users supported? Is there a way around without moving the mailbox to Office 365.