It is common that all smart devices get switched to 2G or 3G network mode if there is no 4G coverage available. But some devices face issues for switching to 4G LTE mode even though there is enough LTE coverage. If you are in middle of such issues, here is an app.
4G LTE Only Mode Switch app helps you to find and search for 4g LTE signal. Once you locked to 4G Mode, no other 2g/3g signals won't be catch by your phone.
This app is very helpful if your device don't have a "4G Only" Mode in phone settings.