For Cisco Engineers:
On an RV134W-A-K9 V01, Firmware 1.0.1.20:
The top/first 2.4Ghz SSID configured under "Wireless>Basic Settings" will always have priority, meaning any WiFi clients connected to it will experience expected WiFi performance. All other 2.4Gz SSIDs and 5Ghz SSIDs appear to be throttled to only use the bandwidth not used by the top/first SSID. This was tested with multiple client types (e.g. MacOS, Windows, iOS), using different VLAN and SSID combinations, using hourly scheduled speed tests over multiple weeks.