[Nut-upsuser] SNMPv3 fails when more than one UPS is configured in ups.conf

[Lee Damon]

New NUT install dealing with three APC Smart-UPS 5000s, two of which
have AP9617 and the third has a AP9619 card.

The SNMPv3 configurations on all three are exactly the same. This is
confirmed by snmpget calls that work just fine:
        snmpget -Cf -v3 -u [...] -l authPriv -A '[...]' -X '[...]' -a
MD5 -x DES [upsname] .1.3.6.1.4.1.318.1.1.1.1.1.1.0

snmp-ups can query all three UPSs with SNMPv1 with no problems. However,
querying with SNMPv3 doesn't work if I try to query more than one of them.

SNMPv3 works fine when I have any one of the three configured in
ups.conf while the other two are configured with SNMPv1. It doesn't
matter which _one_ UPS is configured for SNMPv3 in ups.conf, they all
work individually (see below example).

However, if I configure any two or all three of them to use SNMPv3 then
on startup upsdrvctl complains about "unhandled ASN 0x81 received from
.1.3.6.1.4.1.318.1.1.1.9.3.3.1.7.1.1.3" and fails to start.

My current [redacted] ups.conf follows. The only differences between the
values are on the port and desc lines (ignoring #, of course).

[ups1]
    desc = "APC Smart-UPS 5000 SNMP in rack 1 - AP9617"
    driver = snmp-ups
    mibs = apcc
    port = [ups1...]
#    snmp_version = v1
#    community = [xxx]
    snmp_version = v3
    secLevel = authPriv
    secName = [xxx]
    authPassword = [xxx]
    authProtocol = MD5
    privPassword = [xxx]
    privProtocol = DES

[ups2]
    desc = "APC Smart-UPS 5000 SNMP in rack 2 - AP9619"
    driver = snmp-ups
    mibs = apcc
    port = [ups2...]
    snmp_version = v1
    community = [xxx]
#    snmp_version = v3
#    secLevel = authPriv
#    secName = [xxx]
#    authPassword = [xxx]
#    authProtocol = MD5
#    privPassword = [xxx]
#    privProtocol = DES

[ups3]
    desc = "APC Smart-UPS 5000 SNMP in rack 3 - AP9617"
    driver = snmp-ups
    mibs = apcc
    port = [ups3...]
    snmp_version = v1
    community = [xxx]
#    snmp_version = v3
#    secLevel = authPriv
#    secName = [xxx]
#    authPassword = [xxx]
#    authProtocol = MD5
#    privPassword = [xxx]
#    privProtocol = DES


OS: CentOS Linux release 7.4.1708 (Core)
Kernel: 3.10.0-693.5.2.el7.x86_64
NUT installed from: nut-2.7.2-3.el7.x86_64 (EPEL RPM)

SNMP-related RPMs installed on the host:
net-snmp-devel-5.7.2-28.el7.x86_64
net-snmp-utils-5.7.2-28.el7.x86_64
nagios-plugins-snmp-2.2.1-4git.el7.x86_64
net-snmp-libs-5.7.2-28.el7.x86_64
net-snmp-agent-libs-5.7.2-28.el7.x86_64
net-snmp-5.7.2-28.el7.x86_64


Any suggestions on where I should look next would be greatly appreciated.

thanks,
nomad