[Someone]

Tried that. Cannot reproduce (iOS 15.1; iPhone and iPad).

I have seen iOS on iPad suddenly start with a set of tabs from some time ago, though, and that can look identical to “losing all tabs”. Can’t repro that either, but it seems to happen after one runs multiple Safari’s side by side and then went back to full-screen (if you do that, multiple Safari’s show up in the Task Switcher)

Either way I think this is a bug, not by design.

[joconde]

When I clear history from the Settings app, it closes all tabs (at least it did when I tried a few months ago). When I clear from Safari itself, it doesn't close tabs. Maybe you did the latter?