Orphan processes were not being reaped automatically inside dynos. In a few advanced cases, such as when many child processes are being forked, this may lead to an accumulation of zombie (defunct) processes inside dynos. Zombie processes can cause the max number of processes to be reached and prevent any new processes from being created.
PID=1 process running inside dynos (similar to
/sbin/init on traditional Unix-like systems) will now automatically reap these extra processes, which prevents the accumulation of zombie/defunct processes.