> Well first make sure to go into your settings and enable "Show FPS counter" so that you can accurately determine how much input delay you're dealing with.
I do always have it on and the thing is that it actually shows normal latency (4.3 in main/song select menu and sub .7 in game)
> Try turning off background video
I do have it turned off
> trying a different skin
Doesn't really affect anything
> Or maybe even turning on compatibility mode through settings.
Tried doing that as well, didn't help at all
> Make sure your mouse has the same delay as your tablet.
My mouse does have same delay as my tablet, both get some kind of delay after about a minute of playing
> Might have something to do with your keyboard, operating system, or third party software.
Keyboard is perfectly fine. Talking of operating system, I checked my HDD with DISM and sfc but they have not found anything wrong with my system. And for the 3rd party apps -- I genuely have no idea but it might do something with it, but the thing is about latency increasing ONLY ingame, everywhere else it works just as before.
I will be hard reseting Windows later today. I'll update the post whenever I finish.
Update: it works perfectly after Windows hardreset.