(I'm the author of the library) I'm almost certain you're correct - we (thought) we had compression enabled on our feature builder and never found the root caus

(I'm the author of the library) I'm almost certain you're correct - we (thought) we had compression enabled on our feature builder and never found the root cause, but regardless we're happy with how BTables ended up for the other reasons detailed. For future use cases we'll definitely be re-evaluating HDF5!