It contains issues, but maybe not the issues you're looking for.
Here's the documentation regarding logs, please read it completely:
And also this:
General Web Publishing Settings for Server | FileMaker
You have to enable access logging. Even access logging though won't necessarily log disconnect errors. If you think about it, a user getting disconnected via their side of the connection just looks like any other force disconnect from filemaker server for webdirect (such as closing a browser tab or exiting a browser), so it's not really recording any special events.