Forcefully killing the process was causing build errors, despite the completion of the tasks, so instead I found a neat, temporary solution until the problem get resolved: add a shell script in the middle to remove the --stdin-canary and forward every other args to the real bee_backend executable.
In case someone is having the exact same issue, here are the steps I did to make it work:
#!/usr/bin/env bash
args=("$@")
for ((i=0; i<"${#args[@]}"; ++i))
do
case ${args[i]} in
--stdin-canary)
unset args[i];
break;;
esac
done
${0}_real "${args[@]}"