Nmap SYN Scan blocks all connections?

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 but also didn't get anything suspicious

Any pointers would be appreciated.