Apple - MacBook 4K/60Hz adapter is working directly, but not via USB-C hub

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.