I don't think the bpm is changing. 00:21:645 (1) - , 00:24:845 (1) - , 00:28:045 (1) - 00:31:245 (1) - etc. still fall on the same white ticks for the current bpm. it's just for some reason the sounds after the sliders were (inconsistently) played with a delay
in sb, you can just dim Untitled1 to 0 when you stop using it, and prolong it until the end of the map and use instead of Untitled1 - Copy (hope it's clear enough)
I used a different image for that since using Untitled1 again later would cause the sb load in previous sections to go to 5.33x (causing the text to turn red). I hadno idea what that means but I assumed it was something I shouldn't do; https://osu.ppy.sh/help/wiki/Beatmap_Editor/SB_Load says not to either. For now I'll keep it as is