How to stop iPad in safari from automatically deleting all open tabs when setting is on manual closing only.

I’ve been doing research on my iPad with newest software update. On safari, I’ll open numerous tabs and keep going back and forth between them. Then I’ll get out safari for a multitude of reasons. When I go back into safari, all the tabs are gone. This used to happen occasionally for no obvious reason, but now it seems to happen every time. The tabs are set on manual closure. How do I make it stop automatically closing tabs. I’m even considering getting a different tablet if there is one that doesn’t do this. HELP!