The scripts not able to make the file to size 0, every times it go back to its original size

#!/bin/sh
##########################################################################################################
#This script is being used for AOK application for cleaning up the .out files and zip it under logs directory. 
# IBM
# Created 
#For pdocap201/pdoca202 .out files for AOK
#1. Send and zip the files from /usr/filenet/p8/domains/wlsdomain/
#2. Remove the copied files in /usr/filenet-out/archive
#3. Remove the .out file more than 750 MB
#
#
###########################################################################################################
# Define all date variables
###########################################################################################################
#
tempY=`date '+%Y'`
tempm=`date '+%m'`
tempb=`date '+%b'`
tempd=`date '+%d'`
tempH=`date '+%H'`
tempM=`date '+%M'`
tempS=`date '+%S'`
dt="Date${tempY}${tempm}${tempd}_Time${tempH}${tempM}${tempS}"
###########################################################################################################
# The destination file locations are variable so that it can be changed according to the file system provide.
###########################################################################################################
host_file_location1="/usr/filenet/p8/domains/wlsdomain/fnetServer1.out"
host_file_location2="/usr/filenet/p8/domains/wlsdomain/fnetServer3.out"
destination_file_location="/usr/filenet-out/archive"
logFile="/usr/filenet-out/logs"
 
 
report_filesize1=`ls -l ${host_file_location1} |awk '{print $5}'`
report_filesize2=`ls -l ${host_file_location2} |awk '{print $5}'`
cat ${logFile}/output.log_${dt}
##chmod 777 ${logFile}/output.log_${dt}
echo "filesize1_${report_filesize1}" >> ${logFile}/output.log_${dt} 
echo "filesize3_${report_filesize2}" >> ${logFile}/output.log_${dt}
flag_filesize=768000
echo "print file limit ${flag_filesize}" >> ${logFile}/output.log_${dt}
if [ $report_filesize1 -ge $flag_filesize ]
then
echo "inside if when fnetServer1.out is greater" >> ${logFile}/output.log_${dt}
echo "Coping the fnetServer1.out file to the ${destination_file_location}" >> ${logFile}/output.log_${dt}
cp -p ${host_file_location1} ${destination_file_location}/fnetServer1.out_${dt}
echo "Zip the old fnetServer1.out file to ${destination_file_location}" >> ${logFile}/output.log_${dt}
gzip ${destination_file_location}/fnetServer1.out_${dt}
echo "creating the fnetServer1.out file" >> ${logFile}/output.log_${dt}
cat /dev/null > ${host_file_location1}
echo "Archive of fnetServer1.out complete" >>${logFile}/output.log_${dt}
fi
if [ $report_filesize2 -ge $flag_filesize ]
then
echo "inside if when fnetServer3.out is greater" >> ${logFile}/output.log_${dt}
echo "Coping fnetServer3.out the file to the ${destination_file_location}" >> ${logFile}/output.log_${dt}
cp -p ${host_file_location2} ${destination_file_location}/fnetServer3.out_${dt}
echo "Zip the old fnetServer3.out file to ${destination_file_location}" >> ${logFile}/output.log_${dt}
gzip ${destination_file_location}/fnetServer3.out_${dt}
echo "creating the fnetServer3.out file" >> ${logFile}/output.log_${dt}
cat /dev/null > ${host_file_location2}
echo "Archive of fnetServer3.out complete" >>${logFile}/output.log_${dt}
fi 
#####################################################################################################
# Remove all files from the archive directory that are over 365 days old.
#####################################################################################################
#####################################################################################################
# remove the out files
#####################################################################################################
echo "Removing the out files older than 365 days" >> ${logFile}/output.log_${dt}
find ${destination_file_location}/*.gz -mtime +364 -exec rm -f {} \;
#####################################################################################################
# Removing the log files
#####################################################################################################
find ${destination_file_location}/logs/output.log_* -mtime +90 -exec rm -f {} \;
echo "End LogRemover.sh - `date`" >> ${logFile}/output.log_${dt}
echo "Console Logs have been redirected to output.log_${dt}" >> ${logFile}/output.log_${dt}

the file return back to its previous state after executing the . e.g-- if the current file size is 1 GB and after executing the scriptthe file size is 0. but after some time again it return back to 1 GB. Need help