Thanks Gavin for the immediate reply.
Just as I was about to post a new follow-up, I saw your reply.
I think I found the reason.
I have been using a third-party software to hide (all or selective) windows so that they do not get disturbed by my playful child when I take short breaks in between my Trading activities.
I switched to that software ONLY RECENTLY from another one [which I was using for a long time], because the former is portable while the latter needs installation.
Today I happened to use (start) that software 2 times - firstly before the above Cymatic scenario occurred and secondly after I re-started Cymatic.
I could immediately recognize the obvious impact of that software on Cymatic in the second instance.
So, I am ditching that (free) software and switching to a (free) Virtual Desktop program to serve my purpose.
I think the same could have happened the other days too without me being aware of the exact reason.
So, sorry for the confusion, and thanks for your time.
I believe the situation would not recur.