Just wanted to add another data point for a 2018 P3D+ (VIN: 80xxx) delivered September 2018.
I had a warning pop up similar to others that said "vehicle may not restart. service required" as I had just grabbed some lunch. I wasn't able to take it to the service center right away as I had some meetings back at the office. After I parked it, I heard some abnormal sounds from the battery, and it sounded like the contactors maybe weren't opening/closing correctly. Another error popped up "Electrical system power reduced". At that point, I left it and came back to it 3-4 hours later as I didn't have time to deal with it then and there.
When I got back to it, everything seemed to be fine. Car drove normally, no errors were on the screen. Out of an abundance of caution, I started driving towards the service center and got on the phone to Tesla to see if they could remotely pull the logs. At that point, I was afraid it might be the 12V battery, and I didn't want to get stuck somewhere. Tesla support said they see the errors, but they didn't have additional information, so they also recommended I go to the service center as a drive up (earliest appointment was still 4 days out). As mentioned before, the car drove normally, I was on the highway, easily got up to speed, and nothing seemed out of the ordinary. I got to the service center 10 minutes before they closed and it was a Friday (and they're closed on weekends), so they told me that the earliest they could look at it would be Monday, but were able to get me into a Model 3 Loaner (LR AWD 3 in Chill mode). Below is the timeline of updates after the Friday afternoon drop-off.
Monday: No updates
Tuesday: Got a text saying they had determined there was an internal fault with the rear drive unit and a new one had been ordered, along with an inverter.
Wednesday: I asked about an ETA on parts, and was told while the motor would arrive later in the week, no ETA on the inverter.
Thursday: no updates....got a text saying still waiting for parts.
Friday: Get a text in the afternoon saying parts had arrived, but wouldn't be able to get it done by the time they closed.
Saturday: Get a text from Tesla saying my repair was complete and could pick up the car during business hours.
Monday: I go and pick up the car. Invoice showed drive unit was replaced. Car drove normally (might be a placebo or a week of driving in chill mode in the LR AWD, but my car feels faster?)
Overall, not a bad experience. Thankful to be able to get a loaner. The loaner was not very clean. Had a cigarette butt in the back on the floor (gross!) as pointed out by one of my passengers. Service was communicative, usually would get a text in the early afternoon with progress updates if any. Car is driving great. Unfortunate that the "bathtub curve" didn't really apply to my RDU, but happy to have it fixed.