Huawei Ascend G525 — P 20 lite doesn't play music on headphones.

Check the music player app. Is there some setting option about headphones?

Double-click the Realtek HD Audio Manager system tray icon. Click the small folder icon (see the image below). Check that the 'Disable front panel jack detection' box is cleared. Now insert the jack plug of either a microphone or headphone into the corresponding front panel socket of your computer.
Those little wings you gently bend around cable with just enough pressure to hold it in place firmly. With a knife remove about a 1/2 inch of the plastic insulation from the headphone cable . You will then see 3 colored wires -black, red, and white. On the small wires remove about 1/8 inch of the insulation.

if it is the sofware problem. You will face problem to entire apps. Check your player settings. Are you may reinstall the app