Not 100% sure but I think there's a memory leak in hyperkit. Eventually the memory usage will grow to fill up the allocated space then docker will crash. It might be something else causing it, but that's just what I've observed.
There's also the Docker.qcow2 file ballooning in size. Only way is to do a "factory reset" or running a couple commands to clear out old images.
Not sure where the leak is, but I can confirm there is definitely one there. For me it happens whenever I restart Docker for Mac: 500+ MB of usable RAM gone. Combined with the fact that we don't reboot our Macs very often and that Docker for Mac needs frequent restarts because of hogging CPU otherwise, that's a bit of a problem.
There's also the Docker.qcow2 file ballooning in size. Only way is to do a "factory reset" or running a couple commands to clear out old images.