Tracks are in the root directory, they are name 01.wav, 02.wav, etc.
They were stored in playing order one at the time.
They are from 200 to 3000kb wav files. There is no delay when they are shuffleling in play all or cycling playmode, just when using playFileNum() function. So it doesn't seem a buffering issue?
I'm using the DFRobot_DF1201S library, is there another one for DFPlayer pro?
I'm also using an Arduino Nano Every on Serial1 at 115200 baudrate to drive the DFPlayer Pro.
A 1k resistor is inline on the TX line to the DFPlayer Pro RX pin.