Im not exactly sure. On most watches, if the end links are not perfect, the small movements when wearing a watch cause the end link to rub the watch body and cause the scratches. My Grand Seiko SBGA211 actually does this with its solid end link titanium bracelet, but not nearly as deep or bad.
If I had to hazard a guess, it would actually just be the end link being folded hollow and not being 100% perfect. I don’t think it’s from the installation (it’s possible) as the scratches are vertical, and there wasn’t any vertical motion when putting the links on.
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