我有一台 Thinkpad T460（英特尔® 酷睿™ i5-6300U CPU @ 2.40GHz × 4；英特尔® 高清显卡 520 (Skylake GT2)；Gnome 3.28.2），具有双启动（Ubuntu + Windows-10）和双显示（第二个屏幕通过 HDMI 连接到三星高清电视）。双显示器在 Windows-10 上工作正常。
使用 Ubuntu 18.04.4 LTS（64 位；内核 5.3.0-28-generic #30~18.04.1-Ubuntu）时，双显示有故障：外部显示器上仅显示桌面背景、图标和鼠标指针，但不显示左侧的 Unity 图标和顶部栏（活动、日期、网络、声音、电池、设置、关机（...）按钮）。这导致系统无法使用。一旦断开 HDMI 电缆，一切都会恢复正常（单屏）。
欢迎任何解决此问题的建议...如果有帮助的话，我还可以发布其他终端命令的输出。
Inxi -f 的输出
CPU: Dual core Intel Core i5-6300U (-MT-MCP-) cache: 3072 KB
clock speeds: max: 3000 MHz 1: 1729 MHz 2: 734 MHz 3: 802 MHz
4: 761 MHz
CPU Flags: 3dnowprefetch abm acpi adx aes aperfmperf apic arat
arch_perfmon art avx avx2 bmi1 bmi2 bts clflush clflushopt cmov
constant_tsc cpuid cpuid_fault cx16 cx8 de ds_cpl dtes64 dtherm dts
epb ept ept_ad erms est f16c flexpriority flush_l1d fma fpu
fsgsbase fxsr hle ht hwp hwp_act_window hwp_epp hwp_notify ibpb
ibrs ida intel_pt invpcid invpcid_single lahf_lm lm mca mce
md_clear mmx monitor movbe mpx msr mtrr nonstop_tsc nopl nx pae pat
pbe pcid pclmulqdq pdcm pdpe1gb pebs pge pln pni popcnt pse pse36
pti pts rdrand rdseed rdtscp rep_good rtm sdbg sep smap smep smx ss
ssbd sse sse2 sse4_1 sse4_2 ssse3 stibp syscall tm tm2 tpr_shadow
tsc tsc_adjust tsc_deadline_timer vme vmx vnmi vpid x2apic xgetbv1
xsave xsavec xsaveopt xsaves xtopology xtpr
lshw -c video 的输出
*-display
description: VGA compatible controller
product: Skylake GT2 [HD Graphics 520]
vendor: Intel Corporation
physical id: 2
bus info: pci@0000:00:02.0
version: 07
width: 64 bits
clock: 33MHz
capabilities: pciexpress msi pm vga_controller bus_master cap_list rom
configuration: driver=i915 latency=0
resources: irq:128 memory:e0000000-e0ffffff memory:c0000000-dfffffff ioport:e000(size=64) memory:c0000-dffff
lsmod | egrep ‘i915’ 的输出：
sudo lsmod | egrep 'i915'
i915 1937408 24
drm_kms_helper 180224 1 i915
drm 483328 16 drm_kms_helper,i915
i2c_algo_bit 16384 1 i915
video 49152 2 thinkpad_acpi,i915
xrandr 的输出：
Screen 0: minimum 320 x 200, current 5280 x 2160, maximum 16384 x 16384
eDP-1 connected primary 1440x810+3840+0 (normal left inverted right x axis y axis) 309mm x 174mm
1920x1080 60.02 + 60.01 59.97 59.96 59.93 48.00
1680x1050 59.95 59.88
1600x1024 60.17
1400x1050 59.98
1600x900 59.99 59.94 59.95 59.82
1280x1024 60.02
1440x900 59.89
1400x900 59.96 59.88
1280x960 60.00
1440x810 60.00* 59.97
1368x768 59.88 59.85
1360x768 59.80 59.96
1280x800 59.99 59.97 59.81 59.91
1152x864 60.00
1280x720 60.00 59.99 59.86 59.74
1024x768 60.04 60.00
960x720 60.00
928x696 60.05
896x672 60.01
1024x576 59.95 59.96 59.90 59.82
960x600 59.93 60.00
960x540 59.96 59.99 59.63 59.82
800x600 60.00 60.32 56.25
840x525 60.01 59.88
864x486 59.92 59.57
800x512 60.17
700x525 59.98
800x450 59.95 59.82
640x512 60.02
720x450 59.89
700x450 59.96 59.88
640x480 60.00 59.94
720x405 59.51 58.99
684x384 59.88 59.85
680x384 59.80 59.96
640x400 59.88 59.98
576x432 60.06
640x360 59.86 59.83 59.84 59.32
512x384 60.00
512x288 60.00 59.92
480x270 59.63 59.82
400x300 60.32 56.34
432x243 59.92 59.57
320x240 60.05
360x202 59.51 59.13
320x180 59.84 59.32
DP-1 disconnected (normal left inverted right x axis y axis)
HDMI-1 disconnected (normal left inverted right x axis y axis)
DP-2 disconnected (normal left inverted right x axis y axis)
HDMI-2 connected 3840x2160+0+0 (normal left inverted right x axis y axis) 1872mm x 1053mm
3840x2160 30.00*+ 25.00 24.00 29.97 23.98
4096x2160 30.00 25.00 24.00 29.97 23.98
1920x1080 60.00 50.00 59.94 30.00 25.00 24.00 29.97 23.98
1920x1080i 60.00 50.00 59.94
1680x1050 59.88
1600x900 60.00
1280x1024 75.02 60.02
1440x900 59.90
1366x768 59.79
1280x800 59.91
1152x864 75.00
1280x720 60.00 50.00 59.94
1024x768 75.03 70.07 60.00
832x624 74.55
800x600 72.19 75.00 60.32
720x576 50.00
720x576i 50.00
720x480 60.00 59.94
720x480i 60.00 59.94
640x480 75.00 72.81 66.67 60.00 59.94
720x400 70.08