So, I dug into this a little more and looks to be an exceeded limit on the import or .NET limitation on the number of connections at once.
I pulled this from the Core.BusinessLayer.log, located at C:\ProgramData\Solarwinds\Logs\Orion
2016-07-06 10:09:26,944  WARN SolarWinds.APM.Common.APMBusinessLayerProxy - An error occured when connecting to the communication channel.
2016-07-06 10:09:26,944  ERROR SolarWinds.Orion.Core.BusinessLayer.DiscoveryImportManager - Exception occurred during discovery import
System.ServiceModel.ServerTooBusyException: Server 'net.tcp://<servername>:17777/orion/apm/businesslayer' sent back a fault indicating it is too busy to process the request. Please retry later. Please see the inner exception for fault details. ---> System.ServiceModel.FaultException: There are too many pending secure conversations on the server. Please retry later.
--- End of inner exception stack trace ---
I'm guessing this is hitting the default for maxPendingSessions, which is 128, but odd to see it during the import wizard. The wizard is trying to import 240 devices/nodes at once, so I suspect once it hits beyond this 128 marker, it dies. I'll need to tune the wizard to some how avoid this, but interesting to know what was expected when importing nodes from AD that would exceed this limit automatically.
Has anyone else run into this yet?
I think I am running into this on larger network subnets. Discoveries work fine, but when I tried a manual import on the large subnet, it failed and crashed. I had not dug into it yet except to find this post.