Connthrottle shouldn't kick in unless needed. What I can see from your log file in your post is that the module is doing exactly what it should do: you have set it to 20 per 60 seconds, and it has indeed allowed 20 (even 22) unknown users in and all the known users / SASL could get in too.
Is it normal for your network to see connections from 20 new IP addresses in a minute that have never been seen before?
If you normally have high unknown connection rates, for example if you have a 10,000 user network, then adjust the set::connthrottle::new-users rates
(local-throttle and global-throttle) to suit your network. If 20:60 is not enough, try 40:60, etc...
If the large number of unknown connections is a temporary issue (eg: all your other servers died, and everyone is reconnecting to your server - including many new users), then you can use the following command on IRC (although it only affects the current server where you are connected to as an IRCOp):
If you want to disable a module that is loaded in modules.optional.conf or modules.default.conf without editing that file, you use blacklist-module
in your unrealircd.conf, or elsewhere:
Still, I think connthrottle is pretty neat, it shouldn't be necessary to disable it. Best to just make local-throttle and global-throttle higher (eg: 40:60)