Apple is rolling out a firmware update for the MacBook USB-C Multiport adapter, which improves the compatibility and reliability of affected adapters. These include the Apple USB-C Digital AV Multiport Adapter or Apple USB-C VGA Multiport Adapter.
According to Apple's support website, this update contains the following:
"The USB-C Multiport Adapter Update 1.0 improves the compatibility and reliability of your Apple USB-C Digital AV Multiport Adapter or Apple USB-C VGA Multiport Adapter. This update is recommended for all users."
Enough said, really. If you haven't received an update notification, make sure your adapter is correctly plugged into your MacBook and that you're rocking at least OS X El Capitan v10.11.4. Be sure to have all external devices disconnected from the adapter before you kick off the update process.