That happened with me once, with one of my carded fetts, brought a sliding case and as i was putting fett in i noticed some white showing up on the side so i took it out and a bit white line from the rail edge which cant have been smoothed down properly, so sold it cheap to KFCKarl as couldnt stand it not being perfect
Ever since then i put a cut piece of thin paper under the rail so the card is underneath it and use a ruler to push the card down incase warped
Ever since then i put a cut piece of thin paper under the rail so the card is underneath it and use a ruler to push the card down incase warped