On my s8 dex also won't start.
I bought this hub from china. In the comments there are photos with working dex so there is no problem with compatibility.
I have completely reset my phone
I uninstalled the smartthings app
Wipe cache of all dex applications
I changed the battery modes
I also cleaned usbc with isopropanol
Tests it on aoc monitor and sony tv with connected samsung charger
I don't know what else I can change