MacBook Pro Mid 2012 13” - Screen Issues | Vertical patches in the middle, left and right of the display

My MacBook Pro started having issues with the display about 6 months ago with sporadic vertical patches in the middle of the screen. It used to disappear and reappear on and off for a while. But then the patch became more and more persistent and now its permanent. I am very careful with my devices, so mishandling is something I can rule out. I have bought the device in Jan 2017. And the issue started appearing after about 4 years.

I tried all the NVRAM/PRAM and SMC resets, tried booting into safe mode. I tried one option of GPU switching but that also didn’t work, most likely because this version of MacBook does not have AMD Radeon. I tried reinstalling mac on both the SATA and the SSD I had fitted in. (I have added a 240GB SSD as primary and replaced the optical drive with the pre-existing 500GB SATA moved to its place, and replaced one 2GB RAM with an 8GB RAM, making the total RAM capacity as 10 GB.) I tried reinstalling the macOS on the SSD and the SATA. Nothing seems to have worked so far. The issue appeared after 6 months of when these upgrades were made so most likely the issue is not caused due to these upgrades.

I still think this is not a physical display issue because on some rare occasions, I do see the patch clearing up and the image/text in its background appearing as usual. Probably some internal disconnection causing this or some kind of a software fix that needs to be applied.

Anybody has faced similar issues and do you know of any solutions to this problem?