HI Rahul ,
what do u mean by app devices . all versions of android or it crashes on certain specific devices .
if u are talking about UI not coming up correctly it usually the first reason mentioned below
- devs not using the best practices and recommended guidelines. Might sound simple but this is by far the number one reason. Most devs get away blaming it on "so called fragmentation" of the OS :)
- using deprecated apis ( not so common but stil show some unexpected behaviour on devices from different manufactures )
- using device specific apis ( quite rare ; usually devs who do this already know what they are doing )