Ah, I have found that inserting a "I pause" and using it to open the action menu fixes that step - so presumably the XPath finds the first link with my text, but fails to use it because it is not visible. Umm, just like the error indicates!
Yet again I have to tell myself to read what the error message says, rather than what I think it says
Edit: So the solution was to use 'When I navigate to "View all submissions" in current page administration', rather than 'And I follow "View all submissions"' (per https://docs.moodle.org/dev/Acceptance_testing/Compatibility_changes#And_I_click_on_.22Edit_settings.22_.22link.22_in_the_.22Administration.22_.22block.22 )