I've been having this problem for quite a while now, maybe someone can shed some new light on this particulari issue.
I used to have ISA 2006 and moved to TMG 2010. The configuration was transferred. As expected, TMG operated like ISA did except for one significant detail; TMG has four IPSec tunnels to different endpoints / networks ( ISA 2004 / 2006 and Cisco ) which are operational and usable. However, one or two times a day, each tunnel becomes unavailable for a very short time at different intervals from each other. This issue did not exist with ISA 2006, but the configuration is exactly the same.
I've already checked extensively on the matter of packet loss with my ISP, but the uplink quality is fine. This issue is just a small nuicance, since only monitoring is dropping and impact is low.
I'd appreciate it, if someone can present some sugestions on where to look for a possible cause.