I printed mine with PLA, and I've also found that happens occasionally. I only modified the front design from the original model (here: https://www.thingiverse.com/thing:3707384), not the inside clips, so it might be worth asking the original designer there.
After a few days of use, I'm finding that some cards do not stay clipped in. What filament did you print with, and have you had that problem?
Great case. Printed in a single colour (Prusament Ultramarine PETG) yields very nice embossing, although it doesn't show well in my photo. (edited)