Having lag/stuttering/frame-skipping problems of any kind? Try these in order, and test a song in-game in between each step until you reach something comfortable for you.
If you're still having issues after testing all of these individually, then @ me on Discord.
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-play around with vsync checkbox in options (if you have it on, turn it off. Off? Turn it on). Generally, it should be Off, but if you get straight judgment lines in results (no millisecond drift in judgments and they're showing up as straight horizontal lines), you should change it to the other option.
-disconnect from multiplayer if you're playing single player. No reason to get bogged down by multiplayer.
-try swapping between the normal & hybrid versions. Both versions are built around improvements in performance made available by different computer hardware. You don't know which one is better unless you try both. You can find a download to hybrid version where you initially downloaded FlashFlashRevolution,
on the download page for the game.
-Turn off slideshow desktop backgrounds in Windows 10. The swapping between images in Windows 10, on any monitor, causes a shift in usage priority that impedes FFR & can cause lag spikes whenever Windows attempts to generate a new image for the windows background, even if the desktop background is not viewable.
*To check on Windows 10, Windows Settings (click start menu bottom left, type 'settings') -> search 'background image' -> Set 'Background' to 'Picture', and not 'Slideshow'. Make sure all monitors are using a static image.
-set priority of program (right click FlashFlashRevolution.exe under 'Processes') in Windows Task Manager to 'high' (NOT REALTIME). Ctrl+Shift+Escape or Ctrl+Alt+Delete will get you to Task Manager by default. (Specifically in Windows 10, right click the process in Task Manager, select 'go to details', and then select 'Priority' as HIGH.)
-change in-game framerate to that of your monitor hertz (Hz) or a multiple or half of it. (60Hz monitor? try 120fps, or 240fps, or even 90fps. Some people also report stability with either 55fps, or 59fps settings in-game.) *To check on Windows 10, Windows Settings (click start menu bottom left, type 'settings') -> search 'display res' -> Scroll down to 'Advanced Display Settings' -> will show Refresh Rate (Hz).*
-If you have a 'very nice GPU', go to your FFR installation folder -> META-INF -> AIR -> Open 'application.xml' in Notepad or some other program that can read a text file. Double-clicking the file usually will open it up in an internet browser, so you have to manually right-click and 'Open With'. Once there, edit the text between '<renderMode></renderMode>' to be 'gpu' instead of 'direct' (direct is the default). Save the file, Overwrite the previous application.xml and try again. This forces the game to run it on GPU rather than deciding on integrated graphics.
-If you are an Nvidia user and all else fails, right click your desktop -> Nvidia Control Panel -> Manage 3D Settings -> Program Settings -> Add FlashFlashRevolution.exe (There may be more than one if you have more than one installation of FFR, check the file location) -> Customize FlashFlashRevolution.exe to set Vertical Sync to 'Fast' and APPLY.
-In the same location as the above step for Nvidia users, setting 'Power management mode' to
Prefer maximum performance and applying the changes can assist with lag for some users.
-If you are an AMD (Radeon) user and all else fails, go to Radeon Settings (red splash icon on the up arrow in the taskbar, bottom-right) -> Gaming -> Add -> R3Air.exe (or R3.exe, located wherever you unzipped your FlashFlashRevolution files), and from there, turn ON 'Frame Rate Target Control' and change it to your in-game framerate.
- *(from Hakulyte) If everything else fails, Do either "Windows Key + S" to bring up search, or "Windows Key + R" to bring up the 'run' command, and type 'msconfig'. This should bring up a small window for System Configuration. You will want to go to the 'Services' tab at the top, and hit the 'DISABLE ALL' button, hit 'APPLY', and then restart your computer. After your computer has restarted, repeat the above step one more time without restarting your computer, and then try playing again. This removes any possibility of any other software or program interfering with the game, other than basic hardware and the Operating System. However, it turns off a lot of QoL (Quality of Life) stuff and so it's the equivalent of a tactical nuke. You can turn stuff back on that you need slowly through the same menu.
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Can't be of more help than that, most of the issue is directly caused by Windows 10 OS, and can't be changed. Will add more to this as more specific problems / issue arises from players to help better narrow down solutions.
There's been numerous notices from players that the game runs most optimally on Windows 7, so if a Virtual Machine is an option to you, or you are skilled enough to know what you are doing with dual-booting or booting to a separately installed Operating System, then this might be a preferred solution.