Virtualbox Private network with 3 VMs

I have a Vbox setup. it consists of an ubuntu machine we'll call Master, and a couple of other machines.
Up untill now, I had 3 VMs. we'll call them host1 and host2. host1 is a member of a private network with ubuntu, a network named Vlan1, defined in vbox.
host 2 is is a member of another private network, Vlan2, defined in Vbox.

Everything was ok, the hosts would communicate through the Master with pind and nc and everything was fine and awesome. then, I've added 2 new machines. Kali linux and windows 7. Kali joined Vlan2, while Windows joined Vlan1.

kali could communicate with master, same as host2. windows could communicate with Master as well. The problem is this:
I've noticed sometimes I need to bring the VMs up in a specific order for them to work. sometimes it's from high to low, and sometimes otherwise. I have failed to understand why. any help would be much appreciated.

Thanks.

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