If you have 2 x HDMI monitor, the first HDMI monitor is connected from the HDMI port on the hub. The second monitor is from the primary USB-C/Thunderbolt3 port, with a USB-C to HDMI cable.
If the second monitor is equipped with DVI, VGA or MiniDP, please plug in the USB-C to DVI, VGA or MiniDP cable, such as below:
The MiniDP on the hub supports only MiniDP monitor. It is not compatible with Thunderbolt, DVI, VGA or HDMI monitor, even with an adapter. See the image below for detail explanation.
To achieve the extended view in two monitors, one monitor must be connected either from HDMI port or MiniDP on the hub, the second monitor must be connected from the USB-C/Thunderbolt3 port.