Thanks. I will submit a ticket.
After talking to Support, this is a "common issue when upgrading to 10.6." I would translate that to "known issue", but to avoid picking nits, it is sufficient to say that they were able to resolve the issue by uninstalling several components, rebooting and then re-installing the previously uninstalled components. This per Kenneth, the extremely helpful SolarWinds Technician:
- Checked the path for duplicate DLL files:
- No duplicates found
- Checked polling engine status and it's "Last Database Sync" was recent
- Uninstalled Collector, Job Engine v1 & v2 then rebooted the Server
- Restarted the Server- Reinstalled the Collector, Job Engine v1 & v2
- Checked the Polling and it's now updated
- List resource is now working
Hats off to Kenneth in Manila for his quick response and efficient solution!