One of the problems that may be encountered after MIB load for the device you want to monitor, is it still does not recognize the OID we need.
A check is that the directory where you copied the MIB is among the search directories of net-snmp. This can be checked by using the commands:
net-snmp-config --default-mibdirs snmpget -Dparse-mibs 2>&1 | grep directory