I have this USB-C to Dual HDMI adapter which works a treat:
Much cheaper than the Surface Dock...
At a guess I'd say the problem is trying to run two monitors through that hub - it's probably not designed for that use case.
Try one of these instead:
https://www.amazon.com/gp/product/B089CX3DWZ/ref=ppx_yo_dt_b_asin_title_o01_s00?ie=UTF8&psc=1
I use it to connect my SB2 to two 1080p monitors in my office and it does the job and it's a bargain price too.
Your other option would be the Surface Dock which is a pricey way of doing this...
If you only need to connect two 1080p monitors to the Pro X, you have tons of options using one of the USB-C ports. The Pro X technically supports dual displays at 4k 60Hz, but I'm having trouble finding a good hub w/ DP 1.4. Anyway, here's some Amazon options:
Some cheaper options: (I do not know these brands and can't vouch for quality here, but they have good Amazon reviews)
https://www.amazon.com/Adapter-Thunderbolt-Converter-Compatible-MacBook/dp/B089CX3DWZ/
https://www.amazon.com/Sabrent-Adapter-Supports-Monitors-Compatible/dp/B07H11ZHPW/
https://www.amazon.com/Adapter-Converter-Compatible-MacBook-Samsung/dp/B07QKVY23Q/
More expensive options from brands I've used and had good experiences:
https://www.amazon.com/StarTech-com-2-Port-USB-C-HDMI-MST/dp/B06XPVGQKY/
https://www.amazon.com/Cable-Matters-Multiport-Adapter-Ethernet/dp/B0746P6LPP/ (This one will also give you USB-C charging pass through, USB type-A port and slow/100mbps Ethernet)
That should get you started at least. There's really a lot of options for this. If you still can't find what you want, let me know. I have a list as I've been looking for one myself
EDIT: Noticed I made a mistake and posted the display port version for the last one. Updated w/ the HDMI one