To add.. Try restarting the mib2d/snmpd process
Step 1:Take the PID for reference,
show system processes extensive | match "mib|snmp"
1320 root 1 96 0 20464K 8312K select 0:35 0.00% mib2d
1321 root 1 96 0 15248K 9900K select 0:14 0.00% snmpd
Step 2: Restart the process
restart snmp immediately
restart mib-process immediately
Step 3: confirm the process are up with the new PID
show system processes extensive | match "mib|snmp"
71731 root 1 96 0 15228K 9684K select 0:00 0.00% snmpd
71705 root 1 96 0 20432K 8344K select 0:00 0.00% mib2d