Loss of sync in mode switch to/from full screen

4x p6000 cards with sync ii, Windows 10 driving a 3x3 video wall. This worked perfectly for a year, it appears some random update (pushed silently by IT) affected the ability to seamlessly switch modes from windowed to full screen video. When switching a video from windowed mode to full screen mode, all screens now go blank, flicker, then come back to normal operation taking about 2 seconds. Also, when in full screen mode with the mouse cursor hidden, then moving the mouse to make it appear causes the same blank, flicker, resync. This occurs in both VLC and Windows Media player. I’ve tried various versions of nvidia drivers, I found the sync ii card was running 1.0 firmware and it’s now upgraded to 2.02, all cables are firmly connected, the drivers are now 472.12. It’s wired as per the guidelines with adjustments, simply set mosaic to 3x3 grid and save the config. I’m out of troubleshooting ideas. I can’t find anyone else reporting this. Do I have a one off problem?