as you can see, the first red arrow, from left to right. means that the note has already fallen halfway on the keyboard but there is no key glowing. same as the second red arrow. the third arrow means that C# note hasn't fallen on the keyboard, yet there's already a glowing C# key...
it was taken while the app is running. and alright.
Are you seeing this issue in rendered videos, or just generally while the app is running?
This could potentially be due to the framerate not running fast enough, which could be the case in the general app, but shouldn't be the case during rendering. The notes do look correctly synced with the keyboard on my computers, but I'll also take another look.