I have this issue the longest time (mine is Asus T100 CHI), and this article below seems to resolve it for good!
Basically, you go to Device Manager and disable the Power Management option for Bluetooth. So it is actually the bluetooth problem of Asus tablet, not the keyboard!
<<Always thought the Dock is bad, i bought another bluetooth keyboard to replace it, and then saw the same problem!! then i realize that’s why my bluetooth mouse also seems flaky… now i know it is actually the bluetooth of tablet’s problem (well, not the hardware but the driver and the power saving option, apparently)>>
Try it and i hope it works for you all too!