It seems I enthusiastically chose a larger buffer size that appears to be having some issues on some devices that have a lot of memory pressure.

If you reboot your phone, as awful as that sounds, it will likely fix the issue.

EDIT: I've just submitted an update to Apple that uses a more conservative buffer size.

This aspect is hard to get right: I once used an adaptive buffer size that heeded to memory warnings, but that meant that the buffer filled to lower levels than a conservatively sized buffer.

If only iOS had an opt-in for an *alloc returning 0 instead of these warnings, or at least notifying us of how much space left before we're SIGKILL'ed.

I recently read an article here on HN that briefly touched on memory management under iOS and especially the problem of apps getting killed, maybe it is interesting for you: http://sealedabstract.com/rants/why-mobile-web-apps-are-slow... (scroll down to "How much memory is available on iOS?")