Thank you pmoston,
We have quite a few bugs duplicate of 26394372, it looks like a catchall for rendering issues on virtual screens.
We have found a possible workaround that worked in our lab: resetting the system management controller.
I suspect an inconsistency between GPU settings between SMC and OS at the time of upgrading to 10.12.4.
In any case I'd suggest to try this workaround. The instructions are in
https://support.apple.com/en-gb/HT201295
Please let me know if this helps for you, in case we'll publish the workaround in our FAQ.
Kind regards,
Carlo