Hi,
Discovery use SNMP to discover the devices to recognize them and then add them to DCR. If the discovery process is able to communicate the devices with the correct community string, it will add the devices otherwise the devices will remain unreachable.
Kindly re-enter the community \ SNMPv3 credentials and in the target for the time being specify *.*.*.* in case you have unique community string configure on all of the devices and then run the discovery.
Also, Schedule discovery have its own discovery settings so in case this is schedule discovery, select the schedule discovery, edit it and then re-enter the snmp credentials and the target.
Hope it helps,
Many Thanks,
Gaganjeet
