Borderless Fullscreen Framerate drop on Focus Gain

[Haimoimoi]

There's an oddball behavior that I've only noticed very recently in Warframe.  First, I've been running at 144Hz on a G-SYNC monitor in boarderless fullscreen for years now, with no problems.

When running in borderless fullscreen mode, the in-game FPS counter drops to 60Hz when the game has input focus.  Weirdly, the framerate spins back up to 144+ Hz as soon as I click focus over to a window in a different monitor.  When I click back on warframe, the in-game FPS counter begins to slow linearly until it hits 60Hz.  Now I did recently take an nVidia driver update that might also be at fault.  I also thought it might be the windows, discord, steam, or nvidia overlay, so I disabled them all with no changes in behavior.

It's worth noting that windows/nvidia desktop is set to 144Hz.  I also do not use Vsync (though I experimented with it and framerate caps and the behavior remains the same.)

I can correct the problem and get back to 144+ fps by going to full-screen exclusive mode.  It's not ideal though, since I often like to click off warframe to other monitors.

A little meta info:
nVidia Driver Version: 398.36
GeForce GTX 1080 Ti
Asus Rog PG279Q monitor (primary)

Would love it if this was a simple bug with a framerate cap on focus.  In games I've worked on, we would add a framerate cap when an app loses focus, so we wouldn't be stealing so many system resources when you weren't actively controlling it.  Maybe something like that went haywire?  Anyhoo, feel free to contact me directly about the issue, I'm happy to provide any additional information on request.

[CasualSuperman]

I'm seeing the same issue with a GTX 1070, nVidia Driver Version 398.82, Dell S2716DG

[Shadow8600]

Exactly the same issue. Let us know if you found a fix!