Today I've added this plugin v1.3.4 to my copy of Calibre 8.82 running on Windows 7 32 bit sp2 and set it to display in the "Main Icon Bar". When I start up Calibre the "Book Sync" Icon appears. I have gone "preferences/plugins/sync/Customise Book Sync" and added my Amazon Kindle:-
However as soon as I connect my Kindle the "Book Sync" Icon disappears. I'm a newbie to configuring Calibre so it may be I'm missing something obvious here but would welcome guidance.