The issue persists on Ubuntu 21.10 with Linux 5.13.0-39-generic.

Plugging in Display Port into the docking station wakes up the external screen but does not produce an image (the screen stays black) the builtin screen also goes and remains black until Display Port is disconnected again. Dmesg reports:

```
[  403.810921] [drm] DP Alt mode state on HPD: 1
[  403.883530] [drm] DM_MST: starting TM on aconnector: 00000000c7e4d18b [id: 90]
[  404.002066] [drm:drm_dp_mst_dpcd_read [drm_kms_helper]] *ERROR* mstb 00000000da8e8ece port 1: DPCD read on addr 0x4b0 for 1 bytes NAKed
[  404.094206] [drm:drm_dp_mst_dpcd_read [drm_kms_helper]] *ERROR* mstb 00000000da8e8ece port 2: DPCD read on addr 0x4b0 for 1 bytes NAKed
[  404.937533] usb 4-1.2.4: new full-speed USB device number 36 using xhci_hcd
[  405.057017] usb 4-1.2.4: New USB device found, idVendor=0409, idProduct=04c6, bcdDevice= 0.01
[  405.057029] usb 4-1.2.4: New USB device strings: Mfr=1, Product=2, SerialNumber=3
[  405.057033] usb 4-1.2.4: Product: EA275UHD
[  405.057036] usb 4-1.2.4: Manufacturer: NEC
[  405.160140] hid-generic 0003:0409:04C6.001A: hiddev0,hidraw1: USB HID v1.10 Device [NEC EA275UHD] on usb-0000:06:00.3-1.2.4/input0
[  409.602964] [drm:drm_dp_mst_dpcd_read [drm_kms_helper]] *ERROR* mstb 00000000da8e8ece port 1: DPCD read on addr 0x4b0 for 1 bytes NAKed
[  409.638815] [drm:drm_dp_mst_dpcd_read [drm_kms_helper]] *ERROR* mstb 00000000da8e8ece port 2: DPCD read on addr 0x4b0 for 1 bytes NAKed
[  409.707465] [drm:drm_dp_mst_dpcd_read [drm_kms_helper]] *ERROR* mstb 00000000da8e8ece port 1: DPCD read on addr 0x4b0 for 1 bytes NAKed
[  409.743267] [drm:drm_dp_mst_dpcd_read [drm_kms_helper]] *ERROR* mstb 00000000da8e8ece port 2: DPCD read on addr 0x4b0 for 1 bytes NAKed
[  409.812087] [drm:drm_dp_mst_dpcd_read [drm_kms_helper]] *ERROR* mstb 00000000da8e8ece port 1: DPCD read on addr 0x4b0 for 1 bytes NAKed
[  409.847669] [drm:drm_dp_mst_dpcd_read [drm_kms_helper]] *ERROR* mstb 00000000da8e8ece port 2: DPCD read on addr 0x4b0 for 1 bytes NAKed
[  409.916745] [drm:drm_dp_mst_dpcd_read [drm_kms_helper]] *ERROR* mstb 00000000da8e8ece port 1: DPCD read on addr 0x4b0 for 1 bytes NAKed
[  409.952273] [drm:drm_dp_mst_dpcd_read [drm_kms_helper]] *ERROR* mstb 00000000da8e8ece port 2: DPCD read on addr 0x4b0 for 1 bytes NAKed
[  417.157667] usb 4-1.2.4: USB disconnect, device number 36
[  425.461698] [drm] DM_MST: stopping TM on aconnector: 00000000c7e4d18b [id: 90]
```

(The USB through DP seems to be working - the external screen has a device connected to it via USB)

Connecting via HDMI through the docking station fails in the same way. In that case dmesg reports:

```
[  515.176650] [drm] DP Alt mode state on HPD: 1
[  515.247435] [drm] DM_MST: starting TM on aconnector: 00000000c7e4d18b [id: 90]
[  515.421788] [drm:drm_dp_mst_dpcd_read [drm_kms_helper]] *ERROR* mstb 00000000ea0c2bd3 port 1: DPCD read on addr 0x4b0 for 1 bytes NAKed
[  515.490800] [drm:drm_dp_mst_dpcd_read [drm_kms_helper]] *ERROR* mstb 00000000ea0c2bd3 port 2: DPCD read on addr 0x4b0 for 1 bytes NAKed
[  515.560598] [drm:drm_dp_mst_dpcd_read [drm_kms_helper]] *ERROR* mstb 00000000ea0c2bd3 port 3: DPCD read on addr 0x4b0 for 1 bytes NAKed
[  515.643894] [drm:drm_dp_mst_dpcd_read [drm_kms_helper]] *ERROR* mstb 00000000ea0c2bd3 port 1: DPCD read on addr 0x60 for 1 bytes NAKed
[  515.878214] [drm:drm_dp_mst_dpcd_read [drm_kms_helper]] *ERROR* mstb 00000000ea0c2bd3 port 1: DPCD read on addr 0x60 for 1 bytes NAKed
[  521.725387] [drm:drm_dp_mst_dpcd_read [drm_kms_helper]] *ERROR* mstb 00000000ea0c2bd3 port 1: DPCD read on addr 0x4b0 for 1 bytes NAKed
[  521.761095] [drm:drm_dp_mst_dpcd_read [drm_kms_helper]] *ERROR* mstb 00000000ea0c2bd3 port 2: DPCD read on addr 0x4b0 for 1 bytes NAKed
[  521.796295] [drm:drm_dp_mst_dpcd_read [drm_kms_helper]] *ERROR* mstb 00000000ea0c2bd3 port 3: DPCD read on addr 0x4b0 for 1 bytes NAKed
[  521.831504] [drm:drm_dp_mst_dpcd_read [drm_kms_helper]] *ERROR* mstb 00000000ea0c2bd3 port 1: DPCD read on addr 0x4b0 for 1 bytes NAKed
[  521.866782] [drm:drm_dp_mst_dpcd_read [drm_kms_helper]] *ERROR* mstb 00000000ea0c2bd3 port 2: DPCD read on addr 0x4b0 for 1 bytes NAKed
[  521.902464] [drm:drm_dp_mst_dpcd_read [drm_kms_helper]] *ERROR* mstb 00000000ea0c2bd3 port 3: DPCD read on addr 0x4b0 for 1 bytes NAKed
[  521.937956] [drm:drm_dp_mst_dpcd_read [drm_kms_helper]] *ERROR* mstb 00000000ea0c2bd3 port 1: DPCD read on addr 0x4b0 for 1 bytes NAKed
[  521.973705] [drm:drm_dp_mst_dpcd_read [drm_kms_helper]] *ERROR* mstb 00000000ea0c2bd3 port 2: DPCD read on addr 0x4b0 for 1 bytes NAKed
[  522.008924] [drm:drm_dp_mst_dpcd_read [drm_kms_helper]] *ERROR* mstb 00000000ea0c2bd3 port 3: DPCD read on addr 0x4b0 for 1 bytes NAKed
[  522.044159] [drm:drm_dp_mst_dpcd_read [drm_kms_helper]] *ERROR* mstb 00000000ea0c2bd3 port 1: DPCD read on addr 0x4b0 for 1 bytes NAKed
[  522.079315] [drm:drm_dp_mst_dpcd_read [drm_kms_helper]] *ERROR* mstb 00000000ea0c2bd3 port 2: DPCD read on addr 0x4b0 for 1 bytes NAKed
[  522.114912] [drm:drm_dp_mst_dpcd_read [drm_kms_helper]] *ERROR* mstb 00000000ea0c2bd3 port 3: DPCD read on addr 0x4b0 for 1 bytes NAKed
[  522.150225] [drm:drm_dp_mst_dpcd_read [drm_kms_helper]] *ERROR* mstb 00000000ea0c2bd3 port 1: DPCD read on addr 0x4b0 for 1 bytes NAKed
[  522.185363] [drm:drm_dp_mst_dpcd_read [drm_kms_helper]] *ERROR* mstb 00000000ea0c2bd3 port 2: DPCD read on addr 0x4b0 for 1 bytes NAKed
[  522.221338] [drm:drm_dp_mst_dpcd_read [drm_kms_helper]] *ERROR* mstb 00000000ea0c2bd3 port 3: DPCD read on addr 0x4b0 for 1 bytes NAKed
[  537.155668] [drm] DM_MST: stopping TM on aconnector: 00000000c7e4d18b [id: 90]
```