I want to add new field and replace the one of the existing field value to the newly added field

The below is the input for the config file.. Here i want to grep the date from the one of the line and store into a field(called logdate).. Later i want to create the new field(called log_timestamp) with null value and replace that null value with logdate field value..

For the second line, the log_timestamp field is getting the value from the logdate field.. But next lines it is not getting

My stdin input:

START the log printing 08/08/19 09:10:06 343

PID|THREAD NAME|CPU UTILIZATION|MEMORY UTILIZATION
7066|DestroyJavaVM|0.0|11.3
7072|Reference Handler|0.0|11.3
31204|qtp1459076321-3197|0.0|11.3

END the log printing 08/08/19 09:10:06 831

My config file:
filter
{

     mutate
     {
     add_field=>{"log_timestamp"=>""}
     }
	if [message] =~ /^[-\/]/
    {
            drop{}

    }
    if "START" in [message]
    {
		grok 
			{
            match => { "message" => "%{GREEDYDATA} (?<logdate>%{MONTHDAY}/%{MONTHNUM}/%{YEAR}%{SPACE}%{HOUR}:%{MINUTE}:%{SECOND}%{SPACE}%{NUMBER})"}
			}	
	}
	else
	{
		grok
			{
			 match=> {"message" => "%{INT:Thread_Id}\|%{GREEDYDATA:Thread_Name}\|%{BASE16FLOAT:CPU_Utilization}\|%{BASE16FLOAT:Memory_Utilization}"}
			}
		
	}
	if "END the log printing" in [message]
    {
            drop{}
    }
	
	if "PID" in [message]
    {
		drop {}
    }
	mutate
       {
          replace => {"log_timestamp"=> " %{logdate}"}
       }	
}

Output:
{
"@timestamp" => 2019-08-15T06:19:31.505Z,
"logdate" => "08/08/19 09:10:06 343",
"@version" => "1",
"log_timestamp" => " 08/08/19 09:10:06 343",
"host" => "localhost.localdomain",
"message" => "START the log printing 08/08/19 09:10:06 343"
}
{
"@timestamp" => 2019-08-15T06:19:31.506Z,
"@version" => "1",
"log_timestamp" => " %{logdate}",
"PID" => "7066",
"THREAD NAME" => "DestroyJavaVM",
"host" => "localhost.localdomain",
"message" => "7066|DestroyJavaVM|0.0|11.3",
"CPU UTILIZATION" => "0.0",
"MEMORY UTILIZATION" => "11.3"
}
{
"@timestamp" => 2019-08-15T06:19:31.507Z,
"@version" => "1",
"log_timestamp" => " %{logdate}",
"PID" => "7072",
"THREAD NAME" => "Reference Handler",
"host" => "localhost.localdomain",
"message" => "7072|Reference Handler|0.0|11.3",
"CPU UTILIZATION" => "0.0",
"MEMORY UTILIZATION" => "11.3"
}
{
"@timestamp" => 2019-08-15T06:19:31.507Z,
"@version" => "1",
"log_timestamp" => " %{logdate}",
"PID" => "31204",
"THREAD NAME" => "qtp1459076321-3197",
"host" => "localhost.localdomain",
"message" => "31204|qtp1459076321-3197|0.0|11.3",
"CPU UTILIZATION" => "0.0",
"MEMORY UTILIZATION" => "11.3"
}