Chrome proactively discards tabs that have been unused in the background for some time. It will become more common in Chrome 108.

https://developer.chrome.com/blog/memory-and-energy-saver-mode/

Want to experience it?
1. Tell Mastodon what is on your mind
2. Open a new tab and go to `chrome://discards/`
3. Click 'Urgent Discard'
4. Go back to Mastodon

The information entered is gone.

Bonus: Google Analytics (GA) is able to track discarded tabs.