UDT is broken in so many ways that it's making me cry; I have had cases for months and they have still not fixed the code. There are fundamental flaws in the way it works (I am not talking feature requests here, I am talking that design is not working issues. ).
check for message like this:
2014-04-29 10:12:49,962 [ 27] WARN - ScheduleOrUpdateJob() - job scheduling was aborted (Capability is disabled [N:6407|Layer3|disabled|30|1].) [SolarWinds.UDT.BusinessLayer.Polling.UDTJobManager]
if it fails to poll something from a node for some reason then it decides that the node no-longer supports that functionality. For example if the retrieval of the L3 tables fails for some reason it will stop fetching L3 data and not report this anywhere (other than buried in a logfile, or a check-box on the edit-node page). Instead of rediscovery try going to the edit-node details and checking that it is polling for L2 and/or L3 data
If you have Jumbo frames enabled and/or your SNMP devices return more than ~4K of UDP data then the SNMP library used by UDT will fail. There is buddy-drop for 3.0.1 (not integrated into 3.0.2 but it works for 3.0.2 ) that fixes this.
This is just one of the fundamental design errors: a an assumption by a programmer in one part of the code has ramifications and side-effects throughout the whole product that make troubleshooting almost impossible.
Richard