OHH!!! What about your client devices? Are they IT Owned, or BYOD? Are drivers up to date? During lags, and such, are wired clients affected as well? What is your Switch port utilization, how about switch overruns, drops and bad packets to /from the switched interface?
Band balancing is good! Why turn that off? Do you mean to turn off AP Balancing instead?
Do the issues present when clients are on 5gh and 2.4? or just when on one band or the other. Have you tested with turning off 5ghz? Auto power? have you tried reducing power to minimum levels, and reviewing your clients 'netsh wlan show driver' specs to see if the SNR according to the CLIENT is good? have you forbidden Client BYOD yet? reserving air space to only IT OWNED equipment? How about your channels, are they overlapping at all?