Nimbostratus
CirrostratusAn event similar to what you're experiencing happened at our site, except we were running v11 and single-bladed. When moving the blade to a different slot, no monitor traffic would pass. The absence of monitor traffic was related to the interface definitions not being changed -- while in slot 2, the interface definitions still had 1/mgmt, 1/1.1, 1/1.2, etc instead of 2/mgmt, 2/1.1, 2/1.2, etc). A bug according to F5, but we didn't want to spend time experimenting with this theory -- an iffy Standby was better than none!
In the end, after all the blade RMA's, the chassis was replaced and no issues since. A year later, we discovered that most of the RMA's weren't necessary -- release notes revealed that bogus voltage alarms and other power events were determined to be code flaws and nothing was really wrong with the hardware.