The metadata import for this example works for me.
However, the PDF is currently not automatically attached. SSRN puts wrong information in the HighWire metatag and quite easily one gets an alert page about "unusual download pattern"...
(last time I talked to them this was on purpose because they don't consider Zotero downloads "real" downloads and didn't want to mess with their usage stats. I always thought that was a weird argument, but that's what they said.)
Well, if that was the argument, then Zotero can just use a special link, such that they can subtract this usage from the other usage. They just have to tell us, which special pdf link Zotero should use?
I have no problem with the article from this URL, it is imported as the article (connector 5.0.18; Zotero 5.0.18-beta.2, Windows 10, Chrome 60.0.3112.113)
However, the PDF is currently not automatically attached. SSRN puts wrong information in the HighWire metatag and quite easily one gets an alert page about "unusual download pattern"...
For ex. in this URL http://www.jstor.org/stable/2555816?origin=crossref&seq=1#page_scan_tab_contents
it's downloaded as a web page element, instead of an article element