Other activity plugins have a separate permission for editing called 'manage'. The H5P plugin is missing this, restricting its flexibility compared to other activities (giving editing access to other roles etc). Ref. https://h5p.org/node/109648
1. Add hvp:manage permission for editing activities.
2. Double check that 'quiz' and 'lti' don't have any other permissions in common that 'hvp' doesn't have.