Site tab name to dynamically update on custom mobile app

Hi All,

We are trying to display the tasks count in the navigation panel as dynamic label.It works as expected in web browser .But when we access the same from custom mobile app the tab name is not updating dynamically and it updates only after logout-login.

Solutions tried:

1.We have tried to remove the count if the site is accessed from mobile device using a!isnativemobile() function .Which throw the error mentioned below

2.We have tried converting the label from external expression rule which didnt help much.

Please suggest.