App not responding after chartboost ad click

I have added the chartboost intersitial ad for android unity3d project. Now the ads load correctly and are showing correctly in the scene that i have specified. The issue comes when the user navigates to the ads url. Once the url is opened and if the user uses the android back key to navigate back to the unity3d application, all unity3d UI seems to be non interactive.

I am sure that the unity is not paused at this point as the further android back button activates the quit popup(another UI). Only that even this popup is not interactive.

I am using an Age gate before navigating to the url. The Unity3d version is 5.3.4, with chartboost sdk version 6.3.0.

More Info on the issue: I tried with replacing the app id and app signature to test ad campaign and the issue goes away. This happens only with the app id we use for cross promotion ads. Does this have anything to do with the play store app opening the link to the cross promotion as the test ad opening the url in a browser is working fine.