Nmap SYN Scan blocks all connections?

[Purely Pointless <purelypointless () gmail com>]

I have ServerA (running Ubuntu 12.04 (IP: 10.10.10.200) a KVM DomU of an
also Ubuntu Dom0), that is trying to perform a scan against ServerB-ServerZ
(Mixed OS (IPs:10.10.10.20-199)) using the command: nmap -vv --stats-every
5s -sS -R -p 1-65535 10.10.10.20-199

Now everytime I do this all my connections get blocked on the machine
performing the scan (incoming and outgoing). This with iptables and ufw
disabled, rules flushed etc... I can ping the gateway perfectly before the
scan start and during most of the scan until a point where I lose all
connectivity... At that point I can still access the machine via console
and there is no high loads etc...

Something is wrong with the syn scan... I attempted doing a FIN scan that
worked.

Also I monitored most of the logs using the command tail -f
/var/logs/*.log /var/logs/*.err but also didn't get anything suspicious

Any pointers would be appreciated.
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