From the CubePilot website:
SB005: I2C Storm can cause inflight reboots, (all cube and Pixhawk hardware, including clones and derivatives)
Due to an issue with a bug in the I2C system for ArduCopter for 3.6.10 version and earlier and Arduplane before 4.0
Please ground any vehicles that have not BEEN updated to Arduplane 4.0 or 3.6.11 for Arducopter or later.
This issue has lead to aircraft failing mid flight, and the details can be found in the Ardupilot release notes for 3.6.11.
See full instructions at
https://discuss.cubepilot.org/t/sb-0000005-i2c-storm-can-cause-inflight-reboots-all-cube-and-pixhawk-hardware-including-clones-and-derivatives/2419.