Low volume in specific parts of a song on iPhone

I noticed when I play “Crystal Skies” on my iPhone, some of the parts of the music are toned down? Especially at 1:20 - 1:30 in the music I can notice the volume gradually get lowered. I tried playing the same music on my iPad and the same thing doesn’t happen and tried screen recording it and when I play the screen recording on my iPhone the same thing happens but doesn’t happen on my iPad when I play the screen recording.. The weird thing is the transition is smooth? I’m not sure if it’s a normal iOS thing because I searched it up on google and tried the things they said would work but nothing changes. Is this a software issue or hardware issue? Please be not a hardware issue.. 😞

[Re-Titled by Moderator]

Original Title: iPhone volume lowers?