an ambigous error message when the interpreter not found

/app # /usr/local/bin/dumb-init -- /app/watch.sh
[dumb-init] /app/watch.sh: No such file or directory
/app # /usr/local/bin/dumb-init /app/watch.sh
[dumb-init] /app/watch.sh: No such file or directory
/app #
/app # cat /app/watch.sh
#!/usr/local/bin/bash

while true
do
  time ./runner
  sleep 120
done
/app #