I'm having an odd issue with my Forma. It developed a line of, for lack of a better word, negative pixels going down the screen. At first I thought it was a line of 'stuck on' pixels, as it's most clearly visible when the background is dark, but it's not as simple as that.

When looking at a mix of dark and light backgrounds, it looks like the pixels are reversed: light on a dark background, and dark on a light one.

See the attachment.

It's best visible on a dark background, when it's a clear line of bright pixels going down the entire screen.

Anybody have any idea what the problem might be?
It's most likely a screen controller issue. I suggest contacting Kobo.
That's what I'm afraid of, yes. A screen refresh removes the dark bits, but not the light ones, and a complete bright line is visible for a fraction of a second in the 'flash-to-dark' of the refresh
I had a screen controller problem with my old Sony Reader PRS-505. I had a line on the scree and eventually, it stopped working.
Possibly as "benign" as a badly seated flex connector. But, yeah, better contact CS if it's under warranty.
i had the same issue, originally one 1 vertical and 1 horizontal line, now i got 2 vertical line

see my thread

https://www.mobileread.com/forums/sh...d.php?t=334690

very obviously in black picture.
screen damage. It happened to my two auro ones and one forma.I really like Kobo over Kindle, but the quality is not good，
Your summary judgement on just a few personal experiences is unfounded... and most people would say, inaccurate.
I've seen plenty of photos o Kindles with problems on the screen (not a broken screen). I had a Sony Reader PRS-505 have a screen controller problem and eventually, half the screen stopped working.

Things happen sometimes.