STBC (space-time block coding) is an optional feature in 802.11AC.
It allows a transmitter to transmit multiple copies of data streams using a number of antennas.
It also allows a receiver to select the best copy of data between those multiple copies to improve reliability.
There is an interoperability issue between Chromecast (2015) and Chromecast Audio and some models of 802.11AC routers that use this feature on 5GHz Wi-Fi.
This could result in a slow download of the OTA (Over the Air Update).
If your router is on the list below, please FDR (Factory Data Reset) your
and re-setup on 2.4GHz Wi-Fi.
Once the setup is complete and the update is complete, you can switch back your Chromecast or Chromecast Audio to a 5GHz Wi-Fi network using the Google Home app.
TPLink Archer C7 v1 / v2
Netgear R6100 / 6200/6300
Asus RT_AC66U, RT_AC68W