Is this code running in a web process? The documentation for Task.await_many mentions that if the timeout (default 5000ms) is exceeded, the process that called await_many will exit - maybe this is related to Cowboy handlers proably exit, not being logged or reported anywhere ?
Not directly relevant to this issue, I suspect, but worth calling out - seeking to the middle of a long list repeatedly is expensive. Consider using Enum.chunk_every/2 instead.
