When your phone overheats, the network shifts from 5G to 4G to protect the device. When your phone overheats, cool it down first. The 5G network will come back as soon as it cools down.
Is good lock support going to be available in galaxy m5x, f5x now? Earlier it used to show isn't compatible and now it shows this content isn't available. Try searching good lock on Google and see if the same thing is showing in your device too.