I'd have thought background tab would be written to it's domain-partitioned bit of the cache before being unloaded. I'm very surprised you lose the current state. To be honest, that sounds like a bug.

Tab unloading is by design. The difference is that it happens more often on low-memory devices. I use Chrome, but it looks like they all do it:

https://www.chromium.org/chromium-os/chromiumos-design-docs/...

https://hacks.mozilla.org/2021/10/tab-unloading-in-firefox-9...

https://www.reddit.com/r/ipad/comments/gidzwc/why_does_safar...