If one port works while the other does not, odds are overwhelming this is a hardware issue - contact Dell to have the system repaired under warranty.  
Hello all, One of the USB-C port of my new Latitude 7420 has completely stopped working. Win10 device manager displays a code 43 for UCM-UCSI ACP.  I keep it up to date (Dell update sw, windows update). Just added a Dell WD19S docking station a few days before the issue appeared, and I can't see any other major changes. I've tried to uninstall to device in device manager - it reappears upon boot, still stopped. Reloaded BIOS default setting, no changes. Tried to install the 1.9.x FW, but this was denied (upgrade process unsuccessful). Tried then to downgrade the BIOS to 1.7.x (activate the BIOS downgrade in BIOS), but downgrade is also denied. Tried to find solutions on the web, found some messages about issues seemingly related to BIOS 1.8.x (my version), but I can't change it (BIOS 1.9 was removed from Dell website)... Kind of problematic, I need both my USB-c ports working. Any idea?
Latitude 7420 UCM-UCSI ACP code 43 (dead USB-c port)