I guess your box just gets busy reloading rules all the time with links going up and down. I opened a ticket for this http://cvstrac.pfsense.com/tktview?tn=1282,6
I guess we have to somehow make sure the links go down only if they are really dead and not if a single pings gets lost due to high load on the line. For the meantime can you set your monitor IPs to something that won't fail just to see if your tunnels stay up and this problem is related to the monitoring issue?
I will do this. In my opinion the load balancer is really great and for me works perfect, however when the links is satured the ping response from the link gateways is slow and then cause this problem. It could be better if the load balancer try three or four times and deal with slow responses before considering link down. Set high priority to icmp packets could help, I guess!
Ping the gateways is very secure to determine if the link is up. In the past I´ve tested commercial solutions and this products uses your own hosts to do tests, like 'host1.pfsense.org', 'host2.pfsense.org'.