I actually have very same problem. I'm using 3 different CM keyboards. CM Storm QuickFire Pro on old Mac Pro (since OS X 10.9 and now 10.11; keyboard purchased in 2013) CM Storm QuickFire Rapid-i on 2012 MBPr (OS X 10.11; keyboard purchased last year) CM Storm QuickFire TK on iMac 5K (OS X 10.11 and purchased a few month ago) I have same symptom on Pro and TK. I never had issue with Rapid-i. I even tried Rapid-i on iMac 5K and TK on MBPr. Same problem with same keyboard. LED stays on but keyboard stop responding to keypresses. It happens daily and happens almost 24 hours from last connection/reconnection. It's very consistent on how often it happens. That consistency is not 100% everytime but almost. More like 99%. Duration varied before but it's been consistent for over a year now with El Capitan. I see a couple connections here. Pro and TK use Mini USB and Rapid-i uses Micro USB (I don't believe this itself shouldn't make any difference but having different connector may mean different firmware group that would put Pro and TK in same group but Rapid-i in different group). Pro and TK doesn't have any firmware update but Rapid-i did which I applied as soon as I bought it using Parallels VM running Windows 7 (I think I almost bricked keyboard while updating but I believe try updating again bought it back). Now I'm afraid of purchasing any more CM keyboard for Mac as I'm not sure the one I pick will or will not have this problem. I am currently eyeing MasterKeys Pro S as an replacement for TK but having to spend $130 after already spending $92 isn't easy decision to make. As for Pro which I'm using as my work place, it's my daily routine to unplug and plug it back in the morning. And it's not power issue (I already thought about that) as all 3 computers never go to sleep (they're on 24/7). Pro is connected directly to Mac Pro. Rapid-i is connected via powered USB 3.0 hub. TK is connected via powered USB 3.0 hub for each plug/un-plug but was tried connecting directly to iMac 5K and to powered USB 3.0 hub on MBPr. By the way, my co-worker uses TK on his Dell notebook (he bought it because of me ) for a few years and he never had any issue which lead me to buy it a few month ago. I really hope there's solution to this problem but it looks like CM isn't interesting in finding solution as Mac isn't officially supported platform.