Massive cell damage on every panel, what could have happened?

[rin67630]

just out of curiosity: I met yesterday a guy, who wanted to sell 60 piece of 250W solar panels allegedly two years old and every single one of those showed massive burned through collector fingers on the top of the cells, arranged in a kind of snail trails. The glass and the frames where intact.
Of course, I immediately jumped away, but I just wanted to know.
What could have happened to those panels?
Lightning damage? A backpower surge from the SCC? Just badly manufactured panels?

 

[ArthurEld]

Snail Trails - PVeducation.com

Wondering what snail trails look like? Check out this photo, I took this of some newly installed solar modules that where less than 6 months old. I wasn’t in any way associated with with the installation of these solar modules, I just happen to be invited on a tour of a large megawatt solar...

pveducation.com

 

[rin67630]

I did not notice bubbles like this:
but the silver tracks were definitely browned and visibly cut through by heat.

 

[ArthurEld]

The trails are supposed to reduce output some. Santan Solar sells snail trail panels cheap - https://www.santansolar.com/