Firebase analytics strange issue

We are working on firebase analytics in an Ionic3 app.

we post events as below

this.fbainstance.logevent(screen_view,{screen1:'value of screen 1})

This works fine.

But there is a for loop with which we are forming the second parameter by appending variable values. When we toast it using JSON.stringify we see proper value, but it does not post to firebase console, what could be the problem ?