Anker SoundCore 2 sound aux issue

I have bought a fresh Anker Soundcore 2.
No problem with bluetooth use, with the phone speaker works properly.
Instead I have issue using AUX port with a 3.5mm cable: audio is very, low hardly noticeable, with some interference (despite an high volume from external source, a portable MP3 player that I use often without issue with a JBL Flip Speaker).

How fix it?

Have you tried maybe using a different AUX cord? I have having a similar issue with a no-name speaker and I thought I had a defective speaker until I tried a different AUX cable and realized that did the trick