If you have tried rebooting various components and still see the issue, then it can probably be attributed to rounding. Hue lights use a curve for reporting light intensity, rather than a line, as shown in the post below. 15% light intensity is just a tiny bit of actual Lumen output, so probably takes less than 0.5 watt per bulb to generate. If Hue rounds this down to zero before multiplying by the bulb count, that would explain why Sense reports zero.
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