Is the SNMP service running? It is already having issues for years on DDOS6.x that sometimes it crashes when doing something like changing the ro_community or whatever. Certain commands want to respawn SNMP also to activate changes that by the looks of already seem OK, but SNMP is down.

However performing a manual SNMP stop and then start, might require multiple start tries also as it might not (re-)start at the first try. Can't recall for sure if DDOS7.x exhibits the same, hence always check the status of SNMP.

# snmp status
SNMP is enabled.