I have found strange behavior in GA which I can't explain. Here's a situation.
We are measuring bounce rate on our page as well as avg. session duration as a basic engagement metric. In our initial implementation BR was 55-65%. However, because of a context of the page we decided to implement an interactive event after one minute on page (as an indicator of a person read page content). Bounce rate dropped to ~50%.
But there was another thing. Avg. session duration currently is 01:54 which means really low in context of our page. I know that it is because many people leave the page without another hit sent etc. So we decided to add another, this time non-interactive, event called "closing". This event was fired on page unload. We suspected growth in session duration because many visits has time 0:00. We did a test. We've changed our first event (fired after one minute) so it fired an event every 15 seconds from first minute on page to page unload. It helped. Avg. session duration increased from 1:54 to 4:57 and avg. time on page from 1:31 to 4:22. However I noticed another change. Bounce rate dropped from 46% to 24% at the day of the test.
It brings two questions:
1) If event is non-interactive is it also does not affect session duration / avg. page time metrics? There's nothing about it in the docs.
2) Why we've noticed a drop on a bounce rate? New events were fired after 1 minute on page so it should stay at the same level as before.
We want to implement the change but we're not sure if it falsely lower bounce rate which we don't want.
Thank you in advance.