SNMP intermitted

[Chrisbad]

Hi all. I'm new to Cacti and new to the forum.

I am monitoring a few Cisco switches (same HW and SW) and have great results with all of them except for 4 of them. I am using SNMPv3 and the configs on all switches are the same.
I hope someone here can assist me in resolving the problem.

The symptoms I see on the 4 difficult switches as as follows:

When I go into Console, Devices, click on these devices, I sometimes get information about the device at the top of the screen, but other times I get "SNMP error" in red. These devices also remain in the "Down" state.

When I first added the devices I was able to add graphs, but because the device now remain in a down state the graphs are not being updated/populated.

If I use the Verbose Query, I get sometimes get the SNMP info and other times I get "No SNMP data returned". Below is a extract from the two queries:

Working:

Running data query [1].
Found type = '3' [SNMP Query].
Found data query XML file at '/usr/share/cacti/site/resource/snmp_queries/interface.xml'
XML file parsed ok.
Executing SNMP get for num of indexes @ '.1.3.6.1.2.1.2.1.0' Index Count: 35
Executing SNMP walk for list of indexes @ '.1.3.6.1.2.1.2.2.1.1' Index Count: 35
Index found at OID: 'iso.3.6.1.2.1.2.2.1.1.1' value: '1'
Index found at OID: 'iso.3.6.1.2.1.2.2.1.1.300' value: '300'
Index found at OID: 'iso.3.6.1.2.1.2.2.1.1.1500' value: '1500'
Index found at OID: 'iso.3.6.1.2.1.2.2.1.1.10101' value: '10101'
Index found at OID: 'iso.3.6.1.2.1.2.2.1.1.10102' value: '10102'
Index found at OID: 'iso.3.6.1.2.1.2.2.1.1.10103' value: '10103'

Not working:

Running data query [1].
Found type = '3' [SNMP Query].
Found data query XML file at '/usr/share/cacti/site/resource/snmp_queries/interface.xml'
XML file parsed ok.
Executing SNMP get for num of indexes @ '.1.3.6.1.2.1.2.1.0' Index Count:
Executing SNMP walk for list of indexes @ '.1.3.6.1.2.1.2.2.1.1' Index Count: 0
No SNMP data returned

Any guidance is appreciated.

Chris