My network type inexplicably changed to public for no reason.  I suspect it was some OS update . 

Anyway, did you think i could find out how to change it back ???

In the old days it was easy, network&sharing settings, where it showed the network type and you could change it . 

I followed about 5 different guides on the internet for changing this , and NONE of them worked. 

The way i did this in the end is to change it via homegroup settings .