Yeah, I only mentioned the card details because I wasn't able to use interval timer shooting on a slower card not too long ago. I didn't want anyone to recommend using a faster card as a solution because I don't think that's the issue. Also, I used the same card back in February and shot several time lapses consisting of 800+ exposures without any problems.
I've used various settings, but most recently, I had it set to take four-second exposures at one-second intervals with a maximum of 999 exposures. It only took 243 and by my math, it should've taken around 350 or so by that time.