I maintain that the other processes are, indeed, waiting behind the looping process to be killed.

Yes, just like you asked. Wait for all five processes to end/hang before sleeping ten seconds and re-running all five programs again.

In both of the cases, there's less than 12s between the time the first batch of five finishes and the next one starts, so it's working fine.

Why does it say test4.sh ended at 11:29:37 when it was still producing output at 11:31:39?

Also, again, it would really help if you printed when the processes exited if you're going to keep discussing this.