Sometimes you want to have a conditional widget to appear on your front page and your front page is not a blog as per your WordPress setup. Ok, you fire up Widget Logic, you checked wp_reset_query fix, you tried to include is_home() statement, does not work, you tried is_front_page (), same thing, you stuck.
You googled 1hr in a row and found many threads with similar problem, bad repeatability of the bug. But it exists! Your widget does not appear on front page! WTF!! I can tell you, there could be worse. In my case it appeared on OS X version of Safari, but never appeared on Windows browsers. You know – this is a clue, man!
Switch off your cache plugin and check your front page. If your widget is there – see, switch it back.
Hope I saved you some time