There are two reports of the rate as the field appears twice in the wlan_radio block, once under the wlan_radio.11ac.user (User 1:) block and once under the main block. I'm not familiar enough with WLAN captures to say if this is a dissector error or not, but I would think that there should either be one entry, or there should be different field names. Please raise an issue on the Wireshark Bugzilla for this.