Just tried Firefox; same behavior. If I go directly to the discovery_status.list table, it is clear that they are all either cancelled or active. So it doesn't really appear to be a browser behavior.

My understanding is that this is a Helsinki instance built from scratch not an upgrade. Also it is an on-premise instance.

I went through the event logs and for example, on the most recent SNMP scan I see the sequence of discovery.started, discovery.phase.completed, discovery.device.completed. all within 45 seconds of each other. For today I see 6 discovery.started, 7 discovery.phase.completed and 3 discovery.device.completed.