MonitorActivity processor generates a false positive on a node restart

If the monitoring scope is configured to "cluster", then there are multiple restart cases when markers are incorrectly generated:

CASE 1

• The flow is already inactive, and there is no traffic. The processor is still running and scheduled on all nodes.
• We restart any of the NiFi nodes in the cluster.
• All nodes, except the restarted one, generates activation marker. (Reason for this is, that the common timestamp is updated by the restarted node during initialization.)

CASE 2:

• The flow is already inactive, and there is no traffic. The processor is still running and scheduled on all nodes. Reporting is done by all nodes.
• We temporarily stop any of the nodes.
• We start traffic on any other node, so that an activation marker is generated.
• We start the previously stopped node again.
• This node does not send activation marker. (Reason for this is that the initial state is always active.)

Expected behavior for stop/start cases would be:

• Single node restart alone should not affect the flow activity state.
• If a marker has already been sent before stopping the processor, it should not be repeated on next start, unless asked for, or there is a change in activity state.
• If the flow was active during a weekend shutdown, it should not begin with an inactivity marker right after startup on monday. Although it should send inactivity marker after the threshold has expired since startup.
• If the flow was inactive during a weekend shutdown, it should send activation marker after started up again with traffic.