Comprehensive and Detailed Explanation From Exact Extract:
Universal Device Pollers (UDPs) in SolarWinds are tightly coupled with the polling engine on which they are configured. If the main polling engine fails, custom pollers do not automatically failover; as a result, statistics collection for those UDPs is interrupted. According to SolarWinds documentation:
"UDPs are assigned to a specific polling engine. If the polling engine fails, UDP statistics are not collected until the engine is restored."
"Universal Device Pollers are not supported on failover engines; they do not collect data from hot standby or failover engines." Thus, options C and D directly reflect the official guidance.
References:
Universal Device Poller limitations and polling engine assignment - SolarWinds NPM Administrator Guide, Custom Pollers section

The local NetFlow source provides live (real-time) flow traffic data that is sourced to and from the main polling engine server. This feature is primarily for monitoring the main polling engine's traffic and quickly identifying top talkers and general flow activity on that server.
Reference:
" The Local NetFlow Source shows live NetFlow traffic sent to and from the main polling engine, giving insight into the traffic patterns for the main server. "
- (Network Performance Monitor Administrator Guide, NetFlow Real-Time Tools section)

When monitoring F5 BIG-IP load balancers, SolarWinds Network Insight requires both SNMP for device status and iControl (a proprietary F5 API) for advanced configuration and health monitoring. The SolarWinds guide states:
" After adding an F5 load balancer with SNMP, configure the iControl connection to access additional F5- specific health and configuration metrics. " References:
F5 BIG-IP and iControl configuration - SolarWinds NPM Administrator Guide, Network Insight for F5 BIG- IP section

The most common cause of duplicate flow data in SolarWinds NTA is when source network devices are configured to export both ingress and egress flow data on the same interfaces. This results in the same traffic being reported twice, leading to inflated statistics and duplicate entries.
Reference:
" If you observe duplicate NetFlow data, check the configuration of your source devices. If both ingress and egress flows are exported for the same traffic, duplicate records will appear in SolarWinds. "
- (Network Performance Monitor Administrator Guide, Troubleshooting NetFlow Issues section)

Comprehensive and Detailed Explanation From Exact Extract:
Disabling NetFlow/CBQoS stops flow data collection, resulting in gaps in graphs during the disabled period (A). However, historical data collected prior to disabling is retained in the database (C), so you can still view past flow information.
Reference:
NTA Administrator Guide, "Enabling/Disabling Flow Collection and Data Retention,"
"Disabling monitoring creates data gaps but does not delete historical flow records."QUESTION