To get the deep sleep function and supervisory watchdog playing nicely with each other required a bit of tuning using well placed delay() functions in the code. Previously, all timings could be done using the millis() function, but with deep sleep, this no longer works as millis() does not operate in deep sleep.
The watchdog chip needs to be pulsed regularly with 3.3 v to stop it from pulling the reset bus low and resetting the MCU. This was easy enough when taking wind and rain readings, but slightly more challenging when it came to reading from the BME260 at the 5 minute interval and allowing 10 seconds for a callback from the raspberry pi internet 'gateway'. A bit of trial and error whilst connected up to a 'scope was the answer. The above image shows the Adafruit M0 feather LoRa radio power profile with deep sleep very close to zero between each set of wind readings in red and the watchdog pulse in blue.