This is fascinating (loved the post), but also why I generally steer clear of these new fangled wizard languages. I do not want to discover that somebody changed my 400 byte template to be 402 bytes and now the server is catatonic. Languages that inefficiently allocate and copy strings may be slower, but at least they approach a cliff at no worse than a smooth O(n^2) curve.
This is due to how the Erlang (specifically the BEAM) VM handles strings, not with Elixir. I don’t think many people would consider Erlang to be a new fangled wizard language, rather, they would just consider it a wizard language. I think the author tried to phrase it in terms of Elixir as that is where the popular focus is, but the oddities are in the Erlang VM.
I think the author (and correct me if i’m wrong) is running into issues with ERL_SMALL_IO_BIN_LIMIT due to the way elixir implements strings on top of binaries.