[?]Strange persistent artifact on screen with Knoppix 8.6 after "Suspend-Restart"s

[rajibando]

Yes, friends, I know that I would immediately be advised to upgrade to the latest knoppix. But currently I have some additional packages installed as a persistent set up which would need time to be ported.

So please forgive me for my not being able to follow up on that advice presently.

Regarding the problem:
---------------------------------
For a long time, with 8.6.0, I have noticed that after a couple of system "Suspend"s and restarts an artifact appears, and remains persistently on the screen which is bothersome. It even appears on Screenshots. It is clearly because of a program, but I can't identify which.

When the system is restarted the artifact goes away, only to reappear after the same couple of Suspends-Restarts.

The relevant portions from hardinfo is:
-Display-
Resolution : 1366x768 pixels
Vendor : The X.Org Foundation
Version : 1.20.4
[...]
Monitor 0 : 1366x768 pixels
-OpenGL-
Vendor : Intel Open Source Technology Center
Renderer : Mesa DRI Intel(R) HD Graphics 520 (Skylake GT2) x86/MMX/SSE2
Version : 3.0 Mesa 19.2.1
Direct Rendering : Yes
[...]
-GPU Drawing-
Intel(R) Core(TM) i3-6006U CPU @ 2.00GHz 4x 2000.00 MHz 3481.93

A screenshot of the artifact is uploaded at my drive (since the image couldn't be uploaded/attached here) : https://drive.google.com/file/d/1ZtO...x-pKlSIR0RH-C/
Could I please be helped in removing this artifact from my screen over multiple "Suspend-Restart"s?