A few options here:
Your customer bounced off the page - he visited for a very brief time and left.
This is highly common, you can compare it to your Google Analytics bounce rate.
Your store is being visited by internet bots. There are plenty of bots that scrape the web to gather information. For example - Google uses a bot for site indexing. These are not buyers - they go on your store, pick up the technical info they need and leave. We have a bot filter in place to avoid recording those.
(this reddit thread is interesting)
3) Loading times
The app only kicks in and starts recording after pages finishes loading. Why? because we do not want to interfere with your store loading speed. So on each page, the app would not run, until the page is fully loaded. Depending on your customer (or yourself) loading speeds - this might appear as shorter sessions than they actually are.
The best way to test your app is to visit your store and interact with it.
Then - go back to the dashboard and play your session.