Devilboy - I had the same issue with HiFace 2 in my system (PC server running Win 7/64 + Jriver 17 + Jplay), but changing the buffer size from 1 to 2 samples, solved the problem.
dCS U-Clock and Stello U3 - which are also XMOS chip based designs, just like like the HiFace 2 - also displayed the very same issue, so I concluded that this problem was Xmos chip specific. At least in my system.
dCS U-Clock and Stello U3 - which are also XMOS chip based designs, just like like the HiFace 2 - also displayed the very same issue, so I concluded that this problem was Xmos chip specific. At least in my system.