The current CaptureShop 6.1 software is stable with Sinar M and Sinar 54H.
An old release of CaptureShop software had stability issues with FireWire connection and crashed Mac OS. (Approx 2009, Contax 645 with Sinar M, not H).
A short 90cm long cable with metal ends works fine with H4D-40.
Although my H4D-40 has latest firmware, FireWire connection is not stable using the standard 4 meters long cable supplied by Hasselblad.
I recently bought FireWire repeater and Tether Tools JerkStopper Tethering Kit to see if it can help.
Anyway, I believe it is a Phocus software issue, not in the camera.