MacBook 4K/60Hz adapter is working directly, but not via USB-C hub I have the Apple MacBook 12" (2016) 1,1GHz 256GB Silver and a 4K/60Hz monitor.

I have tried this hardware to connect the displays at 4k/60Hz:


Anker® Aluminium USB C Type C to HDMI Converter, Supports 4 K/60Hz to
HDMI Converter 
Kanaan USB-C HDMI Adapter | USB-C USB 3.1 Type-C to
HDMI Adapter Converter


This works perfectly when the USB-C port is connected directly to my MacBook.

I have only 1 USB-C port on my MacBook. 

When I add a Belkin USB-C hub or even try to use the USB-C port of the Apple Multi-AV adapter, both adapters don't work, they don't provide any video output.

I have these USB-hubs/adapters:


Apple USB-C Digital AV Multiport Adaptor 
Belkin USB-C 4 Port Mini Port Expansion Hub


Am I missing something here? In my ideal situation I'd like to be able to connect my 4k/60hz monitor, 1440p/60hz monitor and the charging cable at the same time, but the 1440p monitor isn't that important. I'd settle with both the 4k/60hz and charging cable at the same time.
The reason that when you plug in your (known to be good/working) USB-C to HDMI video adapters into USB-C hubs is because the USB-C hubs don't pass the video signal that originates from the MacBook Thunderbolt port.

If you need a hub for connectivity and you want to have HDMI output, you either have to get a dock or a hub that specifically passes the video signals like the Anker Premium USB-C Hub with HDMI and Power Delivery.

Apple tried to make everything simpler with having one type of port, but (IMO) they made it more confusing.  A few things to keep in mind:


USB-C is the physical port type.  USB 3.1 is the USB specification that sets the standard for how the port functions
Thunderbolt 3 is the actual port on your MacBook.  It just happens to use USB-C.  
Thunderbolt 3 has many functions built into one connector


Video (HDMI 2.0 and DisplayPort 1.2)
Power Delivery
USB (3.1 Gen 2)
PCIe (PCI Express 3.0)



That's just a quick summary;  for full details, see Thunderbolt 3.

So, just because an adapter "says" USB-C, dosen't mean it's going to carry all those signals/protocols.  USB-C is often gives the end user the perception that "if it fits, it works."  Unfortunately, now you have to verify that that what you want to do is supported by the adapter.