I have an sd card I inserted and mounted on my lg phone and was able to access music files stored on sd card and when done I unmounted and removed sd card. Next day I inserted same sd card on same phone as day before but this time it would not let me access same music files as I was able to the day before. Why is that?
You really shouldn't be removing and reinserting the card. While they technically 'can' be used that way, that leads to damage rather quickly. It is smarter to have separate cards for separate devices (assuming that is what you are doing with the card).