Windows 7 VM freezes for 5 - 10 seconds then resumes

Parallels: Version 13.3.2 (43368)
This issue has only appeared in the last few weeks but I am unable to define exactly when. The Mac is running fine with no sign of a similar problem.

The VM appears to freeze for a short period and then continues. If I am typing the window stops displaying new characters but once the freeze ends it catches up (no characters are lost). If I have the windows clock open the clock stops updating for the period of the freeze (the second hand stops). After the freeze ends the clock catches up. One thing I note is that the Windows 7 Event Log has a lot of these events:

"The system time has changed to ‎2018‎-‎08‎-‎01T13:20:47.494000000Z from ‎2018‎-‎08‎-‎01T13:20:42.585000000Z."

The timing of these messages seems to correspond with the freezes of the Windows 7 UI.

While its an irritation when typing it has more serious consequences when interacting with USB devices that are connected to the VM. Sometimes control of these is lost, probably because the VM did not respond within a required timeout as it was frozen.

I cant rule out the possibility that the issue is with the Windows Guest OS (or some rogue driver within it) but I have seen it occur when no USB devices where attached to the VM. When its not frozen the VM and all its app/drivers/devices work fine (which is much of the time).