I’m not too across all the specifics, but I think there’s some kind of parallel gremlin lurking. I can reliably trigger the HDF5 abort by using 4 or 6 ranks, but I’ve been successful with 2, 3, 7, and 8. My guess is it’s some combination of the masking on tiles and the distribution of the files to process over the ranks? Will dig deeper to get a definitive answer though!