It seems that metadata download from amazon is broken.
I suspect Amazon has changed somethcos Calibre 3.18 also gives no results.
My plugin is configured for Amazon.com site Germany and download from Amazon servers.
Example for an output shows that data is found but not downloaded. Also seems that authors value is not taken for the query even if the field is filled in calibre metadata dialog:
Running identify query with parameters:
{u'title': u'Nebelbr\xfccke', u'timeout': 30, u'identifiers': {}, u'authors': [u'Bomm, Manfred']}
Using plugins: Google (1, 0, 0), Amazon.com (1, 2, 0)
The log from individual plugins is below
****************************** Amazon.com (1, 2, 0) ******************************
Found 0 results
Downloading from Amazon.com took 3.97699999809
User-agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/51.0.2704 Safari/537.36
Server: amazon
Getting details from: https://www.amazon.de/Nebelbr%C3%BCc...1905882&sr=1-1
Could not find title/authors/asin for 'https://www.amazon.de/Nebelbr%C3%BCcke-achtzehnte-H%C3%A4berle-Kriminalromane-GMEINER-Verlag/dp/3839222397/ref=sr_1_1/260-0608862-7896637?s=books&ie=UTF8&qid=1521905882&sr=1-1'
ASIN: u'3839222397' Title: u'Nebelbr\xfccke: Der achtzehnte Fall f\xfcr August H\xe4berle (Kriminalromane im GMEINER-Verlag)' Authors: []
Thx in advance
Martin