Originally posted by WorksAsIntended I see three points.
The simplest one would be the interface between the chip and the panel. They are often line by line, so if you loose a bit of contact this might be the outcome.
More likely the stack of the chip has some errors.
You may look at the chip soldering too.
The lines appeared in groups over several weeks. This seems likely to be indicative, but what it shows I don't know.
Thanks for input. No sure what you mean by "More likely the stack of the chip has some errors". Sorry if being dim.
I checked cables etc were seated OK, but as the monitors not been moved for all that time, this seemed unlikely. The "interface" was where I was thinking. I assumed that some sort of driver chip was controlling portions of the display and that each chip would likely have a cap associated with it.
Does chip soldering fail after time?