Yes, I've had that problem occur before but maybe once in 6 months. I just figured maybe the provider had done something to their routers ?? As for %defaultroute IPsec uses this by default, have a look in /etc/ipsec.conf. Who is your provider? I'm no expert but if your gateway keeps changing maybe your subnet mask might be wrong. It probably should be 255.255.255.252 for a static connection. You'll have to check with your'e provider though.
Cheers Lloyd