Fenix 6 Pro - 20% power drain in 3 hours (update now 8% loss in 43 minutes, proof in photos)

Hi

This morning when I woke up my Fenix 6 Pro was at 84% at 7:30 AM - I cycled into town to get some groceries and used about 1 hour of GPS.

Suddenly at 10:45AM the battery is at 66% and draining rapidly. I always have Bluetooth off (I hate notifications), and I don't use an apps, CIQ or 3rd party watch faces. I've not used any music. I've never turned on the SPO2 sensor (don't see the point of it)

I am on 15.71 beta but the Usage widget isn't showing any signs of abnormal drain. 

Looking at the watch face and doing nothing else shows: 

10:43 AM UK time: 67%

10:45 AM UK time: 66%

11:01 AM UK time: 64%

11:08 AM UK time: 63% (so 4% drain just observing the watch face from 10:43 to 11:08)

Device Usage stats:

Uptime 3d:00:55:20

Low Power: 2d:17:47:16

GPS: 01:01:32

OHR Scan: 00:40:05

ANT Scan: 00:32:51

BLE Scan: 00:32:19

WIFI: 00:04:19

Backlight: 00:00:00

CGM: 00:00:00

The power is draining rapidly as I type but the Usage Widget isn't showing whats doing it. I honestly I hoped I got away from strange and unexplained power drain I used to get from my Fenix 5+, but doesn't look like it. I have hardly anything on the watch left I can turn off.