FIFO and simple bash parallelization on CentOS

Question

I am having problems adapting a bash script to handle a simple parallel execution from Ubuntu 20.04 to CentOS Linux 8. In the script I spawn multiple "readers" that read a string from a FIFO and output it on a common file. The strings are passed to the FIFO directly from the main script. I use file descriptors and locks to make the process clean. I'm also waiting that all the readers start before writing on the FIFO. I'm including the whole script at the end.

The script work flawlessly on Ubuntu, and the output is this (first column is the reader ID, the second is what the reader got from the FIFO)

2 1
4 2
1 3
...
3 4998
2 4999
4 5000

The reading is complete and the messages were transmitted one by one.

Using the same script on CentOS I get this.

4 1
1 7
2 8
...
3 153
4 154
1 155

There is an evident jump, and the messages from 2 to 6 are lost completely. Moreover, the process stops very prematurely at 155.

I really don't know what's going on. Any idea?

The script:

#!/bin/bash
readers=4
objs=5000
echo "" > output.txt
Temporary files and fifo
FIFO=$(mktemp -t fifo-XXXX)
START=$(mktemp -t start-XXXX)
START_LOCK=$(mktemp -t lock-XXXX)
FIFO_LOCK=$(mktemp -t lock-XXXX)
OUTPUT_LOCK=$(mktemp -t lock-XXXX)
rm $FIFO
mkfifo $FIFO
Cleanup trap
cleanall() {
rm -f $FIFO
rm -f $START
rm -f $START_LOCK
rm -f $FIFO_LOCK
rm -f $OUTPUT_LOCK
}
trap cleanall exit
Reader process
reader() {
    ID=$1

    exec 3<$FIFO
    exec 4<$FIFO_LOCK
    exec 5<$START_LOCK
    exec 6<$OUTPUT_LOCK
# Signal the reader has started
flock 5                
echo $ID &gt;&gt; $START
flock -u 5
exec 5&lt;&amp;- 

# Reading loop
while true; do
    flock 4  
    read -su 3 item
    read_status=$?
    flock -u 4  
    if [[ $read_status -eq 0 ]]; then
        flock 6
        echo &quot;$ID $item&quot; &gt;&gt; output.txt
        flock -u 6  
    else
        break # EOF reached
    fi
done

exec 3&lt;&amp;-
exec 4&lt;&amp;-
exec 6&lt;&amp;-

}
Spawn readers
for ((i=1;i<=$readers;i++)); do
    reader $i &
done
exec 3>$FIFO
Wait for all the readers
exec 5<$START_LOCK
while true; do
        flock 5
        started=$(wc -l $START | cut -d \  -f 1)
        flock -u 5
        if [[ $started -eq $readers ]]; then
            break
        else
            sleep 0.5s
        fi
done
exec 5<&-
Writing loop
for ((i=1;i<=$objs;i++)); do
    echo $i 1>&3
done
exec 3<&- 
wait
echo "Script done"
exit 0