"there is a feature that disables f.lux for fullscreen apps, so check if you've set it in f.lux's disable menu."

This was it, thank you so much!

I figured out the issue. Windows 10 has a new "feature" called "Fullscreen Optimizations", which forces every app into borderless windowed mode (!?!). This also explains why all of my games have been getting significantly worse performance since the update.

I haven't figured out a way to disable it globally (none of the suggestions online work), but you can disable it on a per-app basis by finding the executable, right-clicking --> properties --> compatibility --> "Disable Fullscreen Optimizations". After doing this, flux will disable correctly for that application.

Turn off the setting called "Software mouse cursor when needed".

I've got the exact same problem, can't use the dimming feature as well. It's because of the latest 1903 windows update, nothing else. Hope this gets resolved soon!

@herf Ah, just that. Done. Sent. Let me know if there's anything else that'll help you narrow it down.

@nikku I got the latest version as of June 06th 2019 v4.104 and it seems to do the same thing since the May 2019 update for Windows 10 :/

yeah after windows may update this problem happen for everyone
look here
https://forum.justgetflux.com/topic/7021/windows-10-may-update-1903/19

still no fix :(

Open the windows 10 task manager: Shift + Ctrl + Esc key. Alternatively the classic Ctrl + Alt + Del. You may also right click a blank area on the taskbar (where the clock and start menu is displayed) and choose the task manager.

Go to the startup tab and look for f.lux. I've never once had an issue with f.lux nor being in the startup list so if it's not there just reinstall the program.

Night Light is enabled. It's a Windows 10 feature. Turn it off.

I believe this is a false positive.

Impressive that they are removing files from the app store containers. noshow is an extremely small file that just launches f.lux with /noshow.

Pretty sure it is arriving intact - signing is managed by Microsoft.

Yes doesn't work for specific applications either. Would be a great fix.