I came accross this issue when the Port Forwarding rules reached roughly 200.
The problem I had was when I added new rules past 201 (201,202,203 etc.) the Firewall would add them to the interface but the IPtables actually ignored them.
As you can imagine this was incredibly frustrating to the point a second Smoothwall Firewall was installed but the same problem returned.
From chatting with the guys on the smoothwall community ( Smoothwall) they were able to point me in the direct and instructed me to run the following from commandline:
sed -i -e 's=t-/var/log=t/var/log=' /etc/syslog.conf kill -SIGHUP `cat /var/run/syslogd.pid`
Essentially concluded that due to massive log traffic Smoothwall was struggling to write the new port forwarding changes. The above puts a hyphen before each log file name; this is supposed to tell syslogd not to wait for the entry to reach the disk (turns off O_SYNC). The second tells syslog to close, re-read its .conf and reinitialize. If it doesn’t work, you’ll have to reboot when convenient.
I can’t take any credit for this one, “fest3er” came up with the idea on the forum.