Fiora ult/vital not proccing 100% of the time against invulnerable targets.

Duelist Dance vital procs do not seem to proc 100% of the time vs invulnerable targets. https://www.youtube.com/watch?v=xQlyb_WU4Y0&feature=youtu.be It appears this could be related to shielded+invulnerable targets not triggering on hit effects?

Patch 7.24b NA