Windows, flyouts in Photoshop CC 2018 lagging or no longer layering correctly

Photoshop CC 2018, Windows 10, 2 monitors, Nvidia card... no changes in this setup, except that Win10 is new, installed first week of January.

This problem started about 2 weeks ago (March 2018) before I did the latest PS update, and never occurred once before then.

If I have multiple windows open, choosing one no longer brings it to the front immediately - there's a lag of about 5-6 seconds before it appears in front. If I move the selected window, it will sometimes go behind the other(s) and then show up again 5-6 seconds later.

If I open one of the flyouts on the right like Info or Library, it will flyout underneath whatever windows are open instead of on top. Clicking the flyout will not bring it to the top, it stays at the bottom.

What I've done: all drivers on this computer are up to date. I've also gone through the PS performance optimization settings suggested by Adobe and made those changes.