SSL error (ssl_error_bad_mac_read) between LTM and Firefox

We were seeing similar behavior on one of our 11050's, though we are offloading SSL at the F5. It was only affecting traffic coming from our private IP space which was going through a u-turn nat to reach publicly addressed services in our DMZ. The interesting thing is that we were able to remediate the problem temporarily by changing the snat IP on our firewall which was being used by affected clients. Ultimately the behavior returned after about three days using the new snat IP. We also saw similar behavior from Chrome. We failed traffic to another HA member, and the problems subsided. After restarting the problematic member, we failed traffic back to it and it appears to be running clean. We haven't determined the root cause yet. I'm wondering if anyone else has run into this before. (These boxes are currently running 11.5.1hf7)