Could be pressure sender, wiring to that sender, oil pump, bearings, bad filter.

First step is to see what your oil pressure actually is, using a mechanical gauge.

If it only happened once, could just be a glitch. Since it happened soon after you changed the oil, I would look to that. You used an oil which is thinner when cold than the factory recommendation (0 vs 5). That would reduce oil pressure right at startup, as the oil is designed to flow better at very cold temperatures, which you probably dont have this week. Did you change the filter? If so, did you use an OE BMW filter or something else which may or may not have more restriction?

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