I’m sorry to hear about this! You’re not the only user who’s reported some logging problems.
A few things to check:
Have you tried replacing the batteries in the meter? SD cards draw a lot of power when writing, I’ve seen cases where a meter with low batteries will brown out when it attempts to write to an SD card.
Regarding the logging interval:
I should rename this field. The logging interval is the length of sleep between samples, but it doesn’t take in to account the amount of time it takes to wake up and perform the sample itself. So if you set to 1s interval, the meter will wake up, wake the SD card, perform the sample, then set a 1s sleep timer and go to sleep. The wake->sample->sleep time can be quite long. Usually a 1s logging interval results in about 1.2 seconds between samples. If it’s taking 2 seconds that could be indicative of an SD problem. What’s the brand?