I've been trying to figure it out but the wonky hit error bar thing happens at a ton of different BPMs like 120, 180, 200. Is there a better way to find it? I play on a laptop so I doubt it's polling rate is available to look up.
If you get those constant gaps in the hit error bar when playing 120, 180 and 200 BPM maps, that's a symptom of the game running at a multiple of 30 fps (the lower the fps, the bigger the gaps, as long as it is a multiple of 30). It probably has nothing to do with your keyboard.