HPE Nimble SAN - IOs data isn't collected

The standard discovery for the HPE Nimble SAN doesn't provide any graphs for IOs stats, just volume space stats.

Custom IODs to volIoReads (.1.3.6.1.4.1.37447.1.2.1.13) fail to read any data.  (https://mibs.observium.org/mib/NIMBLE-MIB/#volIoReads)

However, when using snmpwalk from the Observium server, it does pull data:

snmpwalk -v2c -c mycommunity nimblesan.domain.int  .1.3.6.1.4.1.37447.1.2.1.13

Any thoughts?