SD card video recording at 2x speed

Last October, I installed 2 new v4 cameras with SD cards. The Events videos play and download at normal speed when viewed. The SD card video plays at normal speed when viewed. But on one camera, SD card video is recorded at 2x speed. So 30 seconds of recorded SD card video gets stored to my iPhone as a 15 second video. Which then plays back at 2x speed. The other v4 camera records SD card video and plays the stored video at normal speed. Any ideas or solutions for this?