As others have complained, I got my seventeenth mote of light (I assume), and they all disappeared. I was fighting the Ascendant Primeval Servitor for my last one, and now I have none. I have linked an image of my inventory to show that I have no Motes of Light, and I have attached an image of my completion of the Visionary triumph.
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here to second this post, i also finished Visionary, got up to 16 motes, and then when i killed the Servitor as my last boss, instead of getting to 17 motes they just suddenly disappeared