This is the same symptom I often get when I try to merge an infinite sequence into a simgle data structure like a map or vector. It very often means that memory was tight and the garbage collector could not keep up with demand for new objects. Most likely the wtr agent is too large for memory. Perhaps you may want to not store the printed results in the atom by changing
(write [out msg] (.write out msg) out)
to
(write [out msg] (.write out msg))