i see a lot of zombie processes as well, i’m using more than 20 ip-addresses. I tried to use on target with the set of ip-addresses and a set of targets with one ip-address per target.
For me the zombies occur only if I scan too many hosts at the same time. As workaround I set “Maximum concurrently scanned hosts” to 5 for every task. Than I am able to scan larger IP ranges without hanging processes.