I have this exact same issue. I have connected two displays (RGB and HDMI cables) I've updated from Ubuntu 18.04 to 18.10. Everything was working correctly in 18.04.

Steps to reproduce:
Case 1:
1. Start docked laptop with displays connected in the docking station
2. Undock laptop
3. Redock laptop -> Freeze/black screen

Case 2:
1. Start docked laptop without displays connected in the docking station
2. Undock laptop
3. Redock laptop
4. Connect display (RGB or HDMI) in the docking station -> Freeze

HW info:
Manufacturer: LENOVO
Product Name: 20HGS27000
Version: ThinkPad T470s
Serial Number: PC0MJA2W
BIOS Version: N1WET51W (Release Date: 09/14/2018)

System info:
$ lsb_release -rd
Description: Ubuntu 18.10
Release: 18.10
$ uname -a
Linux citadel 4.18.0-10-generic #11-Ubuntu SMP Thu Oct 11 15:13:55 UTC 2018 x86_64 x86_64 x86_64 GNU/Linux

Previously installed working versions:
Ubuntu: 18.04
Linux kernel: 4.15.0-38-generic
Network Manager: 1.10.6-2ubuntu1

Logs:
nov 02 12:09:38 citadel kernel: [drm:intel_wait_ddi_buf_idle [i915]] *ERROR* Timeout waiting for DDI BUF C idle bit
nov 02 12:09:38 citadel kernel: [drm:intel_wait_ddi_buf_idle [i915]] *ERROR* Timeout waiting for DDI BUF C idle bit
nov 02 12:09:38 citadel kernel: [drm:intel_wait_ddi_buf_idle [i915]] *ERROR* Timeout waiting for DDI BUF C idle bit
nov 02 12:09:38 citadel kernel: [drm:intel_wait_ddi_buf_idle [i915]] *ERROR* Timeout waiting for DDI BUF C idle bit
nov 02 12:09:38 citadel kernel: [drm:intel_wait_ddi_buf_idle [i915]] *ERROR* Timeout waiting for DDI BUF C idle bit
nov 02 12:09:38 citadel kernel: [drm:intel_wait_ddi_buf_idle [i915]] *ERROR* Timeout waiting for DDI BUF C idle bit
nov 02 12:09:38 citadel kernel: [drm:intel_wait_ddi_buf_idle [i915]] *ERROR* Timeout waiting for DDI BUF C idle bit
nov 02 12:09:38 citadel kernel: [drm:intel_wait_ddi_buf_idle [i915]] *ERROR* Timeout waiting for DDI BUF C idle bit
nov 02 12:09:38 citadel kernel: [drm:intel_wait_ddi_buf_idle [i915]] *ERROR* Timeout waiting for DDI BUF C idle bit
nov 02 12:09:38 citadel kernel: [drm:intel_wait_ddi_buf_idle [i915]] *ERROR* Timeout waiting for DDI BUF C idle bit
nov 02 12:09:38 citadel kernel: [drm:intel_wait_ddi_buf_idle [i915]] *ERROR* Timeout waiting for DDI BUF C idle bit
nov 02 12:09:38 citadel kernel: [drm:intel_wait_ddi_buf_idle [i915]] *ERROR* Timeout waiting for DDI BUF C idle bit
nov 02 12:09:38 citadel kernel: usb 2-4: new SuperSpeed Gen 1 USB device number 5 using xhci_hcd
nov 02 12:09:39 citadel kernel: [drm:intel_wait_ddi_buf_idle [i915]] *ERROR* Timeout waiting for DDI BUF C idle bit
nov 02 12:09:39 citadel kernel: [drm:intel_wait_ddi_buf_idle [i915]] *ERROR* Timeout waiting for DDI BUF C idle bit
nov 02 12:09:39 citadel kernel: [drm:intel_wait_ddi_buf_idle [i915]] *ERROR* Timeout waiting for DDI BUF C idle bit
nov 02 12:09:39 citadel kernel: [drm:intel_wait_ddi_buf_idle [i915]] *ERROR* Timeout waiting for DDI BUF C idle bit
nov 02 12:09:39 citadel kernel: usb 2-4: New USB device found, idVendor=17ef, idProduct=1012, bcdDevice=50.41
nov 02 12:09:39 citadel kernel: usb 2-4: New USB device strings: Mfr=1, Product=2, SerialNumber=0
nov 02 12:09:39 citadel kernel: usb 2-4: Product: Lenovo ThinkPad Dock   
nov 02 12:09:39 citadel kernel: usb 2-4: Manufacturer: LENOVO                 
nov 02 12:09:39 citadel kernel: hub 2-4:1.0: USB hub found
nov 02 12:09:39 citadel kernel: hub 2-4:1.0: 4 ports detected
nov 02 12:09:39 citadel kernel: [drm:intel_wait_ddi_buf_idle [i915]] *ERROR* Timeout waiting for DDI BUF C idle bit
nov 02 12:09:39 citadel kernel: [drm:intel_wait_ddi_buf_idle [i915]] *ERROR* Timeout waiting for DDI BUF C idle bit
nov 02 12:09:39 citadel kernel: usb 1-4: new high-speed USB device number 12 using xhci_hcd
nov 02 12:09:39 citadel kernel: [drm:intel_wait_ddi_buf_idle [i915]] *ERROR* Timeout waiting for DDI BUF C idle bit
nov 02 12:09:39 citadel kernel: usb 1-4: New USB device found, idVendor=17ef, idProduct=1012, bcdDevice=50.40
nov 02 12:09:39 citadel kernel: usb 1-4: New USB device strings: Mfr=1, Product=2, SerialNumber=0
nov 02 12:09:39 citadel kernel: usb 1-4: Product: Lenovo ThinkPad Dock   
nov 02 12:09:39 citadel kernel: usb 1-4: Manufacturer: LENOVO                 
nov 02 12:09:39 citadel kernel: hub 1-4:1.0: USB hub found
nov 02 12:09:39 citadel kernel: hub 1-4:1.0: 4 ports detected
nov 02 12:09:39 citadel kernel: [drm:intel_wait_ddi_buf_idle [i915]] *ERROR* Timeout waiting for DDI BUF C idle bit
nov 02 12:09:39 citadel kernel: [drm:intel_wait_ddi_buf_idle [i915]] *ERROR* Timeout waiting for DDI BUF C idle bit
nov 02 12:09:39 citadel kernel: [drm:intel_wait_ddi_buf_idle [i915]] *ERROR* Timeout waiting for DDI BUF C idle bit
nov 02 12:09:39 citadel kernel: [drm:intel_wait_ddi_buf_idle [i915]] *ERROR* Timeout waiting for DDI BUF C idle bit
nov 02 12:09:39 citadel kernel: [drm:intel_wait_ddi_buf_idle [i915]] *ERROR* Timeout waiting for DDI BUF C idle bit