I have Catalina 10.15, Music 126.96.36.1996 (the Catalina music player), on a MacBook Air 13".
When the song changes, the equalizer settings change. I don't mean that the sliders move; they are where I left them. But the sound changes. (I set the bass high, and the difference is very noticeable.)
Then if I make any change to the equalizer--choose a different preset, or move one of the sliders a little bit--the sound changes back to what I intended. (i.e. it changes to the setting that I have newly chosen--which is usually pretty similar to what I had before the song changed.) The updated sound setting lasts until the end of the song, it seems, and then I have to fix it again.
I don't know what sound configuration it's going back to when the song changes, but it's not the Flat setting.
This is pretty clearly a bug, and hopefully it will be fixed soon. (I submitted a comment on the Apple feedback page, but who knows whether that has any effect.)
In the mean time, does anybody know of a workaround? Is there is some setting that will stop this behavior from occurring?