Double string comparison fails with correct String reporting

So simple and so not working at the same time..

#!/usr/bin/env bash

RES=$(tail -1 $1)
VAR2=$(grep -oh $2 $1 | tail -1)
VAR3=$(grep -oh $3 $1 | tail -1)

#echo "res=${RES} | var2=${VAR2} - var3=${VAR3}"
#exit 0

if [ ! -f $1 ]; then
  echo "Log file not found"
  exit 3
else
  if [[ ${RES} == ${VAR2}  &&  ${RES} != ${VAR3} ]]; then
    echo $RES
    exit 0
  fi
  if [[ ${RES} == ${VAR2}  &&  ${RES} == ${VAR3} ]]; then
    echo $RES
    exit 1
  fi
  if [[ ${RES} != ${VAR2}  &&  ${RES} == ${VAR3} ]]; then
    echo $RES
    exit 2
  fi
  echo $RES
  exit 3
fi

This is a nagios script that helps me to read log files. I call this script (from nagios) with /usr/local/.../read_log.sh OK NOK

If I uncomment

#echo "res=${RES} | var2=${VAR2} - var3=${VAR3}"
#exit 0

I see from Nagios

Status Information: res=Backup of Monday: OK: Backup of CURRENT: NOK
Performance Data:   var2=OK - var3=NOK

Which should be the 2nd IF with exit 1. But it won't and no matter what, it always go for Unable to read output both if log contain OK and/OR NOK