Thanks for looking in to this t0m, the ASIO SDK host was a good idea.
Yes I have made contact with Focusrite, also sent them a compiled version of the Juce Plugin Host Demo.
Their response:
We are already aware of an issue when using the 2nd Generation Scarlett USB driver with [Product Name] - this has been raised with our development team. Unfortunately I can’t give a timescale for a fix but I have added your details to our maintenance case so that you can be notified when this problem is rectified.
So now I’m holding my breath, waiting for them to run it under a debugger.
Yes it is very strange that it works in Cubase & Traction. Also this only applies to 64bit
Could it have something to do with pointer sizes 32 vs 64 bit. Something we are feeding it?
shot in the blind