To be honest, I wasn’t looking for it when I picked the drone up. Anyway, you live & learn and where’s the fun if everything always goes perfectly 
Not a bad idea, I’ll ask them.
Another good tip, thanks.
Is some kind of radio interference a possibility ?
Zooming in, there is a vehicle stuck in the mud at the water’s edge close to point L.
Could there be a sunken steel boat in the foreshore mud causing a magnetic anomaly ?
I really don’t know. The boat is wooden and I have flown near it and around it several times before without any issues. I think a loose or snapped off propeller as has been suggested is the most likely cause.