Leaving a comment about how you loved the fic is very much not bothering the author - as you say, it's nice to know someone cared enough to comment. It's only demanding or guilt-inducing comments that really bother (some) authors.
If you haven't left a comment, do so. It might encourage the author if they know that someone out there is still reading.
Re: What's the etiquette on asking an author for an update?
(Anonymous) 2016-04-13 08:40 am (UTC)(link)If you haven't left a comment, do so. It might encourage the author if they know that someone out there is still reading.
Just don't bug them for an update.