Try connecting a voltmeter, to monitor the actual voltage your Arduino and amplifier have.
Here’s a blind guess (blind because I can’t see a photo of your wiring)… if you’ve used those cheap breadboard wires, maybe they’re acting a small resistors which limit the current. It’s a common problem when people try to built projects using more power, like servo motors and audio amps. That’s why I recommend using a voltmeter, connected to the location where you’re actually using the power.
Yes it is done on breadboard - see this video it explain the problem of song stop playing abruptly.
In the video you will see Arduino Nano connected to Dfplayer and a mosfet to turn it on, there are other componant like ds3231 etc. but I am not using them for this example. but the problem is same even I remove everything and keep only dfplayer and arduino.
you will also see the code in the video its very simple code. I am using mosfet to turn on the dfplayer and then play it.
I welcome any suggestions. by the way I am trying to solder it on proto type board to avoid any loose wiring or loose connection issue.