Rust on edge of standing seam metal roof.

I was wondering whether you were in a salt or brackish water environment. It sounds like you probably are not. There are a lot of things that could have contributed and one is inferior raw material -- metal or coating issues. I am also unsure whether the panel was cut at that end or folded around but a fold may have been too tight or a cost could have been poorly done such as with a saw. There also could have been leak problems higher on the roof.

Edges are almost never coated after cutting. In most cases, factory edges as you have said this is have very clean cuts which do not promote cut edge corrosion. In a site inspection, I would look for any sort of corrosive run-off that has been on the roof, or any reason moisture has been trapped against the edge of the roof. Barring those things, I would want to get samples of the metal to understand the quality of the metal and whether something went wrong perhaps with the paint pre-treatment. Of course, other things could be discovered along the way as well. Have you contacted the manufacturer? Unfortunately, there is just no way for me to diagnose this further without inspection.

I have several panels with rust on the bottom edge, one very badly rusted. What went wrong?picture1.pdf

I live in Oregon, on the west side of the Cascades. Winter is mostly wet and rainy.

I read some about cut edge corrosion, where possibly edge was not coated after cut, or shear was dull. Most of that information from the UK. Is that something seen here stateside?