I just now tested 3.10 r6 with following configuration done through AP UI and this is how it looks in AP CLI config:
rate-limit wlan downlink 20000
rate-limit wlan uplink 10000
rate-limit client dowlink 4000
rate-limit client dowlink 8000
and I tested with single client as well as two clients and I was able to see client as well as WLAN rate limits working.
Will it be possible for you to share the techsupport from the AP to check out what you have in your configuration. If you have done through cnMaestro I hope the configuration is in sync with the AP. I will message you my email id.
It' s the first time i try to set "Usage limits" (bw throttling) on a CnPilot E serie (me too with two E400).
I've tested with 3.10-r6 and 3.10.2-r1
It seems sometimes it's able to enforce it after a reboot or a change of some other parameter on the UI (in this case, limits are respected but with an awful latency of 1000-3000ms) but after a few moments speedtest are unlimited again.