Disk checks with snmp agent: Where does indexes come from?

[sbelkin]

I get the following error message about /boot partition:
Cannot evaluate expression: "Cannot evaluate function "last()": item "linserver.mydomain:vfs.fs.total[hrStorageSize.57]" not supported.".

However for the same partition I don't get this error for: vfs.fs.total[hrStorageSize.32]

I didn't edit any partitions on such a host, so where does indexes come from? Why does it change?

Please could you explain the rationale behind of that?

Thanks in advance.

PS: I use Zabbix 5.0 LTS

Thanks in advance