There can be many reasons for crashing the app, to fix it, you need to follow the following steps.
clear data of instader and log in again. check, if your phone have sufficient space. Update the app if you have an old version. After following the above steps, restart the app. Please make sure it is closed as background app too. If it is still not working then, once un-install and install the latest version and try again. It will start working.