IPSec Problems

Anyone seeing their customers having problems with IPSec tunnels? Its a strange problem where the customer can ping the other end, but are having trouble keeping the IPSec tunnels active. I was able to preference some of our customer routes out of another BGP edge router which solved their problem. The only common issue (so far) is that the issue seems to occur when traffic goes over a Level3 connection otherwise the IPSec tunnels work fine.

Its a rather strange problem though why IPSec is only being affecting but nothing else and I not saying L3 is the reason, but not sure. I opened a support ticket with one of our upstream providers and they mention their own customers have seen similar problems.

Scratching my head on this one!