Pour some of the starter beer on top into a glass and taste it. It shouldn't smell or taste foul. I've never used WLP400, but her sister, WY3944 is very similar. It never smelled or tasted bad, and none of the sulphur Hefe yeast can throw. It is possible your 400 got infected or was mishandled at some point before you put it on the stir plate, but it is unlikely that happened during those last 24-36 hours. Infections incurred in starters usually manifest themselves later, after pitching.
I had a small reclaimed batch of 3944 Wit yeast that had grown a pellicle. It started to smell really bad after a few weeks so I tossed it.
I had a small reclaimed batch of 3944 Wit yeast that had grown a pellicle. It started to smell really bad after a few weeks so I tossed it.