47 volts on a 18650 based lithium battery is about half charged (3.6V).. . A basic BMS will shut off if any individual cell group dips below 2.5v, while the ebike controller will trip when the battery voltage falls below its LVC, around 41V, Battery sag could cause either to happen, Maybe a broken contact on one group. Maybe a bad contact if you built your own battery using the spring based connectors instead of spot weld. If they are all even though, it's not contacts.

How many amps can your controller pull?

I've been riding more and more when it's below 45F, sometimes at freezing, and it does seem like I an getting more voltage sag when it's cold. I have a bike with the LCD3 display that shows voltage, so I can watch it,

.