Device Manager error in Cisco

Recently, when we try to open Device Manager to make changes on the MDS 9710 switch, the error below pops up.  It only happens to one of the sites.  The other site works fine.  We try to open device manager thru NDFC and get the same error.  

We did see a different error in the past and needed to switchover the controller in the past.  The error was "Busy network, no route, or snmpd is unresponsive."

See EMC kb 000218149.  However, it still fails to open.  

We suspect something with network but still open a ticket with Cisco.  Support runs some trace and does not see issue on the switch side and there is connectivity between switch and the client running Device Manager.  Eventually, we workaround the issue by confirming TCP is set to true for DeviceManager.bat.

set JVMARGS=%JVMARGS% -Dsnmp.preferTCP=true

We still have trouble after that.  So, we login to the switch in the other site that we don't have issue with.  Then click Device > Preference.  

Select TCP for Use SNMP on next launch. Click Apply then Ok.  

Now, try to use Device Manager on the switch that we have issue.  Now it works fine.  Only problem with the workaround is to have a switch that can connect to Device Manager without issue.  I have not asked support if there is any other way to force it to use TCP instead of UDP.