I witnessed a nearly lost stud on my Schwalbe Marathon Winter tyre:
I simply pushed the stud back in. Apparently this is common until the studs bed in, but I think it’s a bit of a weak thing to say, there is clearly a design flaw with these tyres. That aside I keep buying these tyres as there isn’t much alternative here in the UK and I wouldn’t be without them. I try my best to minimize stud loss by checking my tyres regularly for nearly lost studs and also by avoiding dragging tyres and cornering too quickly (probably for the best in winter anyway).
I do have a nice stash of used studs in an old tyre, so I can replace any that do get lost, I also passed some onto a friend of mine who’d lost a few.
It is worth mentioning that these tyres are a real life saver in winter and I wouldn’t be commuting via bicycle in winter without them.