I just tried powering the dfplayer with a different power supply with similar results. Everything works fine until I receive a data packet. Could it be that when receiving a data packet, the RFM9x library does something that causes the dfplayer to reset? I have sent a "test message" as well that does not trigger any of the if-statements, just to see if the dfplayer resets when receiving any data packet and it did. Thanks for taking the time to trouble shoot with me by the way.