Fairford spare wheel problem

Hi Everyone, whilst traveling to a site at Bridlington, in our 2017 Peugeot Fairford the van for some reason dropped it's spare wheel. 
We heard loud noises form the rear of the van, then a car behind was flashing me.
I pulled over, and it was being dragged on the road attached by the lowering cable.
The weather was really bad, late in the evening, and I struggled to understand how firstly it happened. Then how to wind in back into position. We called a breakdown assistants the next day to check but they couldn't find any fault. Has anyone ever come across this problem before or can offer any insight.

As you will have found out as you wound it back up, there is a last quarter turn which 'locks'. Can only presume that it wasn't wound up to the 'lock' twist.


Perhaps you could introduce yourself ...
[You must be registered and logged in to see this link.]

Thanks for your advise, much appreciated.
It would appear, the final twist to lock it properly seated, and periodically checking is the way forward. 
Regards Paul.