Custom eventemitter in ionic range component is not working on production

I wrote 2 eventemitter inside the ionic range component code like “ionStart” and “ionStop”. These events works fine on running on device but not on production release. I figured out that on production release or if i run on device with --prod flag, the observers of my custom eventemitters are empty as you can see in the image below. I spend lots of time to solve this issue with no success. Please help me!