Errors on android version 4.4 and also some on 7.0


I have android version 5.1 on my device I build the whole app using it but when I use my app on my friend’s phone which has 4.4 as the android version the app design disturbs
In version 7.0 design is same but some icons that I made using fontfacetypeCustom(Mateialicon.ttf) have vanished or shown differently
for ex:- I used an Icon named as phone android I put it as phone_android and it works perfectly in my device but when it runs on 7.0 it shows the icon related to phone and android both
Can any tell me why this happens and how to Improve it


i have an app and it has a only webviewer in it.
when the screen initialize webviewer go to url.
i have same issue with 4.4 and 7.0 .
everyday crashes .