The legendary upgrade to the helmet 'Reaper's Helm' doesn't add the mask filter to voiceover from Eivor. Since it's previous tier it only appears as a regular mouth covering mask I'm guessing that is where the problem lies. But currently when it is enhanced to the highest tier (Mythical) it still doesn't add the filter to Eivors voice, which means that the voice just sounds regular like Eivor doesn't have a mask covering his face.