I have a laptop attached to a USB3 docking station, and two monitors attached to that. Total of three screens in my setup. After the screens go blank due to inactivity, *sometimes* when I come back, the dock-attached screens sparkle, and/or randomly go black for 2-3 seconds. "Sparkle" means there is "noise" on the screen; some pixels, or small rows/columns of pixels, randomly light up for a brief moment (like, less than 1/4 second). They appear to only light up with a single color (R, G, or B; never yellow, or white).
Unplugging and re-plugging an HDMI cable for one of the external monitors fixes the problem....until the next, or some future, idle period.
Here's a snippet of inxi, if that helps:
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System: Kernel: 5.15.0-100-generic x86_64 bits: 64 compiler: N/A Desktop: Cinnamon 4.8.6 wm: muffin 4.8.1
dm: LightDM 1.30.0 Distro: Linux Mint 20.1 Ulyssa base: Ubuntu 20.04 focal
Machine: Type: Laptop System: Dell product: Inspiron 5570 v: N/A serial: <filter> Chassis: type: 10 serial: <filter>
Mobo: Dell model: 0YDF7T v: X06 serial: <filter> UEFI: Dell v: 1.14.0 date: 04/06/2023
Battery: ID-1: BAT0 charge: 28.6 Wh condition: 28.6/38.8 Wh (74%) volts: 12.9/11.4 model: SMP DELL 35RH35C type: Li-ion
serial: <filter> status: Full
CPU: Topology: Quad Core model: Intel Core i7-8550U bits: 64 type: MT MCP arch: Kaby Lake rev: A L2 cache: 8192 KiB
flags: avx avx2 lm nx pae sse sse2 sse3 sse4_1 sse4_2 ssse3 vmx bogomips: 31999
Speed: 600 MHz min/max: 400/4000 MHz Core speeds (MHz): 1: 814 2: 1505 3: 700 4: 741 5: 700 6: 700 7: 700 8: 700
Graphics: Device-1: Intel UHD Graphics 620 vendor: Dell driver: i915 v: kernel bus ID: 00:02.0 chip ID: 8086:5917
Display: x11 server: X.Org 1.20.13 driver: amdgpu,ati,modesetting unloaded: fbdev,vesa
resolution: 1920x1080~60Hz, 1920x1080~60Hz, 1920x1080~60Hz
OpenGL: renderer: Mesa Intel UHD Graphics 620 (KBL GT2) v: 4.6 Mesa 21.2.6 direct render: Yes
