You need to also use Pitons to climb up alongside the Buckler. In a few days I'll be uploading a new patch that makes this part of the tutorial easier (this part of the tutorial made more sense back when blocking was a more complicated mechanic).
I figured this out eventually. I think maybe putting in one sentence saying "place the pitons above you and move by using the shield to avoid knockback" would help or something like that. I honestly didn't even realise what to do until I realised my character was jumping up.
