Easy thing to check. Look at the contact point that touches the spark plug top. It is way up in the coil boot. If it looks dullish-gray, it is an indication of a bad coil. Replace all 6 at the same time. Keep the old ones that don't show the dullish gray as spares (keep one in the X with you).

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Kirk
Las Vegas
2016 X5 40e Mineral White/Black Dakota Leather, ZLL, ZCW, ZDA, ZDB, ZPP, multi contour seats, rear side window shades, HK stereo
2011 E90M3, 6-speed manual