Does the AV Multiport adapter charge big MacBook Pros?
Turns out that you can see in About This Mac &gt; System Report &gt; Power
If the power cable is connected to the MacBook Pro directly:
AC Charger Information:

  Connected:    Yes
  ID:   0x7002
  Wattage (W):  94
  Name: 96W USB-C Power Adapter
  Manufacturer: Apple Inc.
  Charging: Yes

and if it's connected through the Multiport adapter:
AC Charger Information:

  Connected:    Yes
  ID:   0x7002
  Wattage (W):  55
  Name: 96W USB-C Power Adapter
  Manufacturer: Apple Inc.
  Charging: No

So if it's looped through the adapter it's only getting 55W which is not enough for the big laptop to charge.