Something is weird, indeed. On Microserver Gen8/ESXi6.0 I can use Jun's loader for install as many VMs as I want, but on other hardwares/ESXi 6 it works only one time.
For the second VM I have to add a second virtual NIC and it works.
For baremetal installs: first DSM ok, for second DSM I have to put a second NIC onto the motherboard - no matter what vendor's mobo I use.
Weirdest thing: setup finished, DSM runs fine, I configure both NICs to use static IP, both work. No matter which one I remove - DSM becomes inaccessibe.
Router reboot, clear DHCP, ARP, reboot everything, clear everything - no use. I move the DSM into a different network: it's safe to remove any NIC I choose, DSM still work.
And all of them is totally independent from routers, I tried pfSense VM, Draytek, Linksys, Windows DHCP...
Funny, really, but in any case a second NIC always helps to get through.