Are you using a Mac for formatting cards? I was getting no recordings for some cards. The red and green LEDs would blink once at the proper recording time, then the green LED would resume blinking, waiting for the next recording time. A card formatting problem was discovered: https://www.openacousticdevices.info/support/sd-card-support/formatting-on-mac If not on Mac, maybe there is a utility or similar way to get more formatting details for your cards to check this.