Horizon Client >4.2.0 Web Browsers White Screen

As the title i'm battling this issue in my homelab, I have horizon 7.2 setup and humming along nicely *apart* from this.

For some reason whenever I connect to my RDS farm through horizon via the thick client under Windows **only** Firefox/Chrome/IE/Edge refuse to render a page. Firefox just spins the loading icon for a moment then stops to a white page, the rest are very similar apart from sometimes Chrome seems to work.

Even more wierdly if I connect with Linux, OSX, BLAST browser or iOS/Android it works perfectly! I can even drop off a non functional windows session connect via any one of the other methods press F5 and the web page that previous was a blank screen renders as normal.

Reverting to 4.2.0 client also fixes this, I've had a look through the release notes for everything after that and can't see anything that stands out as a possible cause. Firefox in debug mode etc doesn't show anything out of the ordinary frustratingly, the rest of the UI works fine its just the actual rendered page section that goes blank.

Anyone experienced this before? Or could give me any pointers? This is just a trial in my lab so a support ticket isn't going to happen. I can't find anything googling around either so i'm guessing I've done something stupid or this would everywhere.