This seems similar to Entire Page Build Disappears with One Click, Saved History Gone.
Again, not sure if I actually did delete something then navigate away (or, for example, the Arc browser will close tabs after 24h). Really unfortunate that it seems that the free plan offers no option to help with this?? My company certainly intends on paying for WeWeb after we do some initial design work, but the lack of any backup option seems quite anti-consumer.