Note that this one, when fetched with MS Edge browser, produces a TXT file (!sic!) which upon inspection turns out be (binary) PDF file, so the mime type and/or headers are definitely wrong with that site/URL.
Way to reproduce: Google Scholar search for Qiqqa Manual and then leaf through their results until you find this one:
Sample URL which fails:
http://52.74.19.76:81/index.php/IJALIS/article/download/48/38
Note that this one, when fetched with MS Edge browser, produces a TXT file (!sic!) which upon inspection turns out be (binary) PDF file, so the mime type and/or headers are definitely wrong with that site/URL.
Way to reproduce: Google Scholar search for Qiqqa Manual and then leaf through their results until you find this one: