That’s weird. It could very well be a memory problem if for some reason the chip wasn’t ‘writing’ the frequencies digitally correctly/fully. Then there would be small gaps in the playback, which digital components don’t handle well. If you ever send a program into “free space” they do some weird stuff. Also if you’re putting a lot of effects into the looper you could be exceeding the memory of the pedal, or forcing it to compress the file, possibly leaving bits of non-continuous data places, which would cause something like you’re hearing I think. If the new memory card fixes the problem, it could just be the old chip didn’t get completely wiped for some reason and was playing small bits of a past recording, so the got a weird transpose of data. That’s all just speculation, though.

Is it working fine still?