This problem happen to me several times. Drop from 4g to 3g (like making call), and it stuck on 3g. Usually i solve this by switching the network mode to 2g/3g and back to 2g/3g/4g to get back to 4g. Airplane mode not solve this. But the much worse is sometimes I cant even change the network mode. It says I am able to set on 3g or above for 1 sim card only. And i only use 1 sim card on slot 1. Please refer my screenshot.
