Player will not recognize sd card content

Hey everyone, I’m new here, let me try to explain this, it’s kinda confusing.
I have two Sansa clip zips, they are several years old, one I use everyday at work and it has about 1000 songs on the 8 gig sd card, I noticed that it wasn’t holding a 8 hour charge like it used to, so I decided to start using my other mp3 player that is rarely used. I took the SD card out of the one and put it in the other and the player says the SD card is empty.
Wondering why the exact type of player does not recognize the content of the SD card and the other one does???
Any help would be much appreciated.

Im not sure but maybe the one micro sd card is formatted for that one special device.

Just like with a nintendo switch.