You’ve configured Cluster SSH and defined a nice list of alias so you hit several boxes easily. BUT, when you call a given alias, nothing happens, but cssh eating up all your memory.
Solution is really easy: do NOT ever name an alias the same as an existing machine name (your DNS resolve).
Say you defined ftp root@ftp root@ftp2 root@ftp3
It’ll fail.
define ftp_servers root@ftp root@ftp2 root@ftp3 and you’re done.