SCP loop stops executing after some time - bash

Question

So I have these two versions of the same script. Both are attempting to copy my profile to all the servers on my infra ( about 5k ). The problem I am having is that no matter which version I use, I always get the process stuck somewhere around 300 servers. It does not matter if I do it sequentially or in parallel, both version fail and both at a random server. I dont get any error message (Yes I know Im redirecting error messages to null now), it simply stops executing after reaching a random point close to 300 servers and it just lingers there doing nothing.
The best run I could get did it for about 357 servers.
Probably there is some detail I unknow that is causing this. Could someone advise?
Sequential
#!/bin/bash
clear
echo "$(date) - Process started"
all_count="$( cat all_servers.txt | wc -l )"
while read server
do
scp -B -o "StrictHostKeyChecking no" ./.bash_profile rouser#${server}:/home/rosuer/ && echo "$server - Done!" >> ./log.log || echo "$server - Failed!" >> ./log.log
done <<< "$( cat all_servers.txt )"
echo "$(date) - Process completed!!"
Parallel
#!/bin/bash
clear
echo "$(date) - Process started"
all_count="$( cat all_servers.txt | wc -l )"
while read server
do
scp -B -o "StrictHostKeyChecking no" ./.bash_profile rouser#${server}:/home/rosuer/ && echo "$server - Done!" >> ./log.log || echo "$server - Failed!" >> ./log.log &
done <<< "$( cat all_servers.txt )"
wait
echo "$(date) - Process completed!!"

Answer 1

Let's start with better input parsing. Instead of parsing a bash herestring from a posix command substitution via a while read loop, I've got the while read loop running through your server list directly via pipeline (this assumes one server per line in that file. I can fix this if that's not the case). If the contents of all_servers.txt was too long for a command line, you'd experience an error and/or premature termination.
I've also removed extraneous ./ items and I assume that rouser's home directory on each server is in fact /home/rouser (scp defaults to the home directory if given a relative path or no path at all).
Sequential
#!/bin/bash
clear
echo "$(date) - Process started"
all_count="$( cat all_servers.txt | wc -l )"
while read server
do
scp -B -o "StrictHostKeyChecking no" .bash_profile rouser#${server}: \
&& echo "$server - Done!" >> log.log \
|| echo "$server - Failed!" >> log.log
done < all_servers.txt
echo "$(date) - Process completed!!"
Parallel
For the Parallel solution, I've enclosed your conditional in parentheses just in case the pipeline was backgrounding the wrong process.
#!/bin/bash
clear
echo "$(date) - Process started"
all_count="$( cat all_servers.txt | wc -l )"
while read server
do
(
scp -B -o "StrictHostKeyChecking no" .bash_profile rouser#${server}: \
&& echo "$server - Done!" >> log.log
|| echo "$server - Failed!" >> log.log
) &
done < all_servers.txt
wait
echo "$(date) - Process completed!!"
SSH keys
I highly recommend learning more about SSH. The scp -B flag was unknown to me because I'm used to using SSH keys and ssh-agent, which will make such connectivity seamless (use passwordless keys if you're running this in a cron job).