Selected fields in splunk UI are not getting saved, each time again we need to select the fields once logging again to splunk UI.
The user configuration known as "selected fields" is located in $SPLUNK_HOME/splunk/etc/users//user-prefs/local/ui-prefs.conf and is modifiable by interface.
Users can change the default user-prefs.conf file that you set.
The choice is
fields = ["host","source","sourcetype"] in display.events.fields
https://docs.splunk.com/Documentation/Splunk/latest/Admin/Ui-prefsconf#Display_Formatting_Options