Why does Samsung s4 Lollipop changes from 2g to 3g and 4g constantly?

[AC Question]

And why does 4g network stop working during calls and the phone does not automatically change to 2g or 3g during them? I guess those two are the reasons for battery drainage...

 

[itguyjax8430]

And why does 4g network stop working during calls and the phone does not automatically change to 2g or 3g during them? I guess those two are the reasons for battery drainage...

Welcome to Android Central!

Try wiping your cache partition to see if that fixes the issue. A lot of phones are having a lot of issues after the update to Lollipop. Wiping the cache partition may fix it. If it does not you may need to do a factory reset to really ensure the issues are fixed.

To wipe the cache partition, follow these steps:

Turn the device off.
Press and hold the following three buttons at the same time:
Volume Up key
Home key
Power key.
When the phone vibrates, release the Power and Home key but continue to press and hold the Volume Up key.
Continue holding the Volume Up key until the Android System Recovery menu displays and then release. This step may take several seconds.
Press the Volume Down key to highlight 'wipe cache partition.'
Press the Power key to select.
When the wipe cache partition is complete, 'Reboot system now' is highlighted.
Press the Power key to restart the device.