Update: Seems to only happen with Erlang 20.3. After downgrading to 20.2.2, everything works again. My other project on the same machine was using 20.2.2. When I upgrade Erlang there to 20.3 it’s broken, too.
I’d like to raise this as a bug somewhere, but I’ve no idea where. I don’t know if it’s an issue with Erlang, Ecto, Postgrex, Poolboy, …
