damn, good that that works, but bad that it confirms that something in 1.6 is the problem
So I still don't know why it's happening, I'll keep looking into it. There's still several possible causes since a lot changed in 1.6. Worst case scenario is that the only fix is basically re-writing the entire note spawning and timing code. Hopefully I can find a simpler solution so I don't need to do that since that will take quite a while.
I don't want to leave you unable to play Ch4 maps until then though. While I can't back-port all of the features of 1.6 right now, I have managed to put just the Ch4 maps in, so I've updated that build with them. The only other change is actually one of the possible causes, I changed the audio on all maps to use the ogg format instead of mp3. This is since they let me compress it smaller while still sounding good, and if I didn't, the file size would be over the Itch.io limit, so I literally couldn't upload the game. I knew oggs were smaller from the start, but I chose to use mp3s since they are less computationally intense to play, so have better performance, and back then there weren't enough maps to hit that limit. So it's possible this doesn't work because of ogg's worse performance, but if it doesn't that will at least confirm the cause of the problem (although, if that's the cause... I'm not sure there's not much I can do to fix it...). So let me know if it works! If it doesn't I'll revert it back to just the actual 1.5 update so you can at least keep playing the pre-ch4 maps