You didn’t mention which camera model(s) you’re using, but I think what you’re describing has been a known issue that plagued some Cam v3s but more recently has been reported to affect some Cam Pan v3s and even some Cam v2s. This happens when you’re trying to view from an event screen (which you get to by tapping a notification or by tapping an item on the Events tab), so the work-around for now seems to be navigating directly to a camera’s microSD card recording timeline (from that camera’s Live Stream screen) and reviewing the event there.
If you navigate to the camera’s Settings ➜ Advanced Settings, you should be able to tell if there’s a card in the camera and, if so, how it’s set to record. Tapping Manage MicroSD Card on this screen should provide additional information.