We’ve got (or should I say, had) a decent amount of woodchip wallpaper in our house form the previous owner.
The thing that made the difference to getting it off was one of those scorers that timba links to above.
It still wasn’t easy, but it did allow the steam to penetrate the paint and top layer of wallpaper and get to the glue underneath.
I think you are better off spending a longer to start with using one of those scorers and absolutely cover the paper, rather than give it a quick whizz round & crack on with the steamer.
Oh, and if you get one of those scorers, wear safety glasses when using it. Bits of paint will chip off and are a nightmare to get out of your eyes…