The issue may be due to syncronization issue between the MDS.
The issue is desynced accounts between the MDS.
If the device have the following configuration in your device,
username admin password 5 $1$fNoCR0ju$mINGwMT041l3eXVvy451S/ rolenetwork-admin
snmp-server user admin network-operator auth md5 ***** priv *****localizedkey
As you can see, "network-admin" in the first line, changed to "network-operator" in the second line, the restored a backup
configuration file and this fixed the problem with FM access.