I have a similar problem. I am running Firefox on Windows 7. When I try to clip a PDF web page, evernote suggests reloading endlessly.
The following log message is output at every attempt, but I'm not sure if it is relevant.
/n23:39:23 GMT+0900 (WARN) moz-extension://f71ced89-6b0e-478b-bae8-97d13d3419e7/background.html: Unable to toggle clipper, tab loaded, but main coordinator is not
B/<@moz-extension://f71ced89-6b0e-478b-bae8-97d13d3419e7/js/main/Extension.js:3:11423
Firefox 60.0.1 (64-bit). Evernote Web Clipper 6.13.2.