We've tried a few things but it hasn't really helped.

When it goes offline I get the following error on the Flint 3:

    # dmesg | grep -i '54:EF:44:5C:BC:B1' | grep kicked
    [3356208.016938] wlan: [0:I:ANY] [INACT] vap-0(wlan0): [54:ef:44:5c:bc:b1]station kicked out due to excessive retries associd 4 (from target) reason 1
    [3363271.980807] wlan: [0:I:ANY] [INACT] vap-0(wlan0): [54:ef:44:5c:bc:b1]station kicked out due to excessive retries associd 4 (from target) reason 1

I had some devices with similar (I think) problems when I did my last round of AP upgrades and tried to do roaming extensions...

I think I'm still running r, but k and/or v were problematic for a few of my clients.