I had the oil sensor replaced in mine, when I had these symptoms. Not sure they should've kept filling with oil w/o checking first though....in other words, oil level may have been fine, but the sensor was reporting incorrectly, so now perhaps there's too much oil?
'11 Z4 30i (Sold!);'11 X3 28i (Sold!); '15 M235i (Recalled/Crushed!); '15 28i X3 loaded; '14 x328i loaded & Mineral Grey '16 M235i Perf Edition, Dinan Stage 2 & CAI