GradleDaemon sometimes redundantly runs in the background and Grails gives erroneous responses. The simplest solution is to kill all the errant GradleDaemon processes and run the app again. Below is a simple script which will run all the errant GradleDaemon processes. The same can be used for killing any processes like say Firefox. Just substitute GradleDaemon with firefox.
# Kills all GradleDaemon processes without mercy
ps -Aeo pid,command|awk '{$1=$1;print}'|grep -v grep|grep GradleDaemon|xargs kill -9