Intermittent flickering horizontal white lines on the display of MacBook Air

On resuming to work on my Macbook Air (2017) from sleep, I noticed horizontal white lines flickering on the laptop display. The lines increased until they filled almost the whole screen rendering the laptop unusable. As suggested on Apple support, I have performed SMC reset, NVRAM/PRAM reset, and reboot to Safe mode several times. I have run Apple Diagnostic test few times and it doesn't report any hardware issue.

I conducted a test where I connected the laptop to external TV using Thunderbolt to HDMI adaptor and the display on the TV looks fine. So, the issue does seem to be with either the display or its connector to the motherboard or both.

At the authorised Apple repair service centre, the serviceman performed all above steps again, but it did not help. Then, he unscrewed and opened the back cover and performed what he called as the display connection reset viz. disconnecting battery connection, then removing the thin display cable multi-pin connector. He cleaned the surfaces with a brush and connected everything back together as rebooted.

But, still to no avail. It is not the backlight or flexgate issue that is happening with Macbook Pro 2016-2018. Changing the angle of the display does not correct the problem.

I have neither dropped the laptop nor spilled any liquid on it.

However, when I returned back home and rebooted, I did see the white lines on the screen at first as before, but they were very few in number this time. After some flickering, they disappeared and right now as I am typing this post from the same laptop, I don't see any white lines, yet.

Probably, the road bumps on the way home, might have done some magic. But, I am not sure when the issue will return back suddenly.

To me, it appears to be some loose connection issue.

Slowly, it fills whole screen like below: