all RAW files disappear when starting import

It sounds like you are using Lightroom Classic, not Lightroom. Lightroom Classic can copy or move images on import, and clearly that is what happened. The images were moved to another folder. That is a choice that you made (at the top of the import dialog) when you imported the photos. Lightroom just did what you told it to do.

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Right,
I've just foud them. Lightroom has created a new folder (named today's date) which it's tagged on to a folder from last week.
Why does it do this (it's not the first time)? No wonder people are leaving Adobe for other software.