If you see a “?” in front of a device and it does not have the device name (or any other information for that matter), then we have a general SNMP communications failure with the device. This means there is an incorrect community string, or a firewall blocking, or we need to add a trusted SNMP host inside the device.
If you see a “?” in front of a device and you DO see the name and some other information (but not necessarily all info), then it means we have good communications with the device, but it failed to respond to some of our queries along the way. We can then get a debug capture of the device to try to determine what failed, and then add it to LLDPDisable.cfg, CDPDisable.cfg, CiscoDisable.cfg, etc. to have it not try to collect that information from that device.