I solved the nagging issue on LXDE. It seems that after power ON from suspend, if the program drawing the window is identified, and the window frame is resized, the artefact vanishes. In many of the cases, pcmanfm creates the artefacts. The issue of artefact took much time to be solved. Perhaps my brain is showing me a sign of its ageing.

I offer my apologies for the typo, writing Artefact as Artifact. Overlooked it completely until now, even with spellchecker ON. Another sign!