Sorry, I thought that at first too, but that is wrong. The "overnight" drop is visible as a small vertical jerk of about 1% difference in the "Battery State of Charge" graph right after the 300 miles mark.
That's why in my account I have the "expected around 90, saw 50 in bad lighting, misread it as 90" snafu. There is a drop, but not as precipitous as it seems.
What happened at 400 miles is apparently a set of full stops as he pulled in to a parking space to talk on the phone and say "I'm not gonna make it," followed by a short reversal of highway time which ends on the 400 mile mark as he went into Norwich, followed by a lot of stop-and-go driving in Norwich to get to some Tesla charger which the NYT article says is around here:
I can somewhat imagine his impatience and wish to get going again, if that's the situation.