Netcat uploads hanging after a certain point

I'm working through an introductory cybersec challenge that requires me to upload a word and brute force a 4 digit code to a port. I put the combinations in a file, and tried to use netcat to upload them one at a time. At a certain point (around 6300 uploads) netcat stalled and stopped uploading things. I ended up splitting the list of number in half, but does anyone know why it would do this? My bash script is below for reference (pass blanked out for obvious reasons).

pass=xxxx
for i in {0000..9999}
do
    echo $pass' '$i >> options.txt
done

cat options.txt | nc localhost 30002 >> flag &