If Ambly honors the default of :print being println then this sample below would be the behavior. Perhaps this is a non-issue because Ambly startup can override this default so that :print is print.
(As an aside, flush is often only needed in combination with print, as oftentimes streams will flush on newlines.)
ClojureScript:cljs.user> (print "Hi")
Hi
nil
ClojureScript:cljs.user> (println "Hi")
Hi
nil
ClojureScript:cljs.user>
For reference, here is the correct behavior
user=> (print "Hi")
Hinil
user=> (println "Hi")
Hi
nil
user=>