regression to Oculus 2017 LTS Windows XR?

VR gets really jerky in windows standalone app after 2nd/3rd time of enabling and disabling VR for Oculus.
After a long wait it can settle down but, but this wait gets longer and longer after each XRSetting.enableds re-enable.
It never used to happen.
It is either down to a Unity regression or changes to Oculus drivers.
Thought .32 might fix but the line below seems unrelated
XR: Fixed null dereference access to vr eye texture manager instance. (1115371, 1171504)

 

One fix for this it to do XRSettings.LoadDeviceByName("") to unload Oculus as well as disabling it, then Reloading the device next time.
However this means the oculus goggles display the shop in the mean time...