I am suffering from quite similar issue on my new iMac 4K. I bought my UR22 last December and it works perfectly with my Macbook Pro (Mid-2012). But with my new iMac 4K, UR22 randomly gets silent or pop noises, which can last almost 1 minute when playing audio or using my Logic Pro X. Particularly with my Logic Pro X, the software shows error message about synchronization error, sampling rate error and incompatible error. And it seems the problem only happens when playing audio/video or using samplers. I have not seen any problems with software synthesizers so far. The more weird thing is that after updating the YAHAMA USB Driver v1.9.6 the problem is getting worse! I really hope Sternberg can solve the problem. If the problem can not be solved in next 3 months I am really thinking switch to other company’s devices.