For me it works perfectly fine. But you may be trying to do a different thing.
Is it a point-to-point link that you are monitoring or is it an AP with many connected users?
Do you use the OID 1.3.6.1.4.1.14988.1.1.1.2.1.3 ?
It is correct that you need to walk it because there are labels below this OID per connected station.
Maybe Zabbix is confused by the funny name (constructed out of the MAC I think) per connected peer.
I have no idea why this is used, but Ubiquiti does it as well.