All Safari tabs have disappeared - twice in 2 days!

I am running iPadOS 16.6, on a pretty new iPad 10th generation, and all my Safari tabs have disappeared, TWICE in 2 days. I have never had this problem before on my iPad Air 2. What is causing this, and how do I prevent it? (I have “Close Tabs” set to Manual in Settings.) I manually restored all the tabs I wanted yesterday, only to find they are no longer there today! I have just manually restored the tabs again, but have totally lost confidence that they’ll continue to be there tomorrow. Any help will be much appreciated.