I would not say it is a definite problem. What I stated (restated here using other words) was that on rare occasions, someone who feels they need your boots/ shoes more than you might, REPEAT MIGHT, take them. It happens...
The Camino, writ large, is very safe. The problems that do occur relate mostly to nuisance things like this. The occasional clothing item or towel disappears from a communal clothesline. A personal item left lying on a bunk "goes walkabout." Electrical adapter plugs an chargers get left behind and sometimes disappear.
But, hospitaleros are, as a group, very helpful. I have seen them place valuables in taxis to get them to the albergue in the next town so the pilgrim who lost the passport, credential, or other item can be reunited with the item. Do not worry. But, also, do not be overly attached to material items.
The Camino attracts all manner of people. That is the nature of the undertaking. In my experience 99.9 percent of all pilgrims are honest, diligent, caring and helpful people. But, we ARE talking about human nature here. One must undertake the Camino with their eyes wide open and not leaving all their street smart behind, at home.
Ideas I can offer to lessen the likelihood that YOUR footwear will be interesting to another person include:
- Do not place your boots/shoes at eye height on the communal rack. Place them so eyes are not drawn to them.
- Tie your shoelaces together so someone cannot slip the shoes on without taking extra time to untie them.
- With #2 above, loop the laces through the rack to "tie" the boots to the rack. It is not a lock, but is a deterrent.
- In 2014, at Roncesvalles, I actually saw someone use a small luggage lock to connect their two boots together using two eyelets. At the time, I thought this a very clever idea...just sayin...
On the other hand, last year, on the coastal route from Porto, a walked with a fellow who had his beloved long-term owned, resoled forever, work issued boots "borrowed" from the boot rack an albergue at Ponte de Lima. They were there when he went in in the evening, and gone when he awoke the next morning. He wore his auxiliary sports sandals on Camino, until he reached a larger town with a good shoe store where he bought a replacement pair of hiking footwear. It does happen, but not to everyone, and not on a regular basis.
Do not be paranoid. In the unlikely chance you do lose something you need, there are outdoor shops all along the Camino. There are Decathlon sports department stores at Pamplona, Burgos, Leon, Ponferrada. Footwear can be replaced. I regularly buy clothing when I determine I forgot something, or something gets misplaced.
I note that other forum members with FAR more experience than me often state that one should not bring anything on Camino that you cannot afford to lose. The above discussion touches on this point. Your stuff does not define you. In my case, my adopted color scheme sort of does, but I digress...
That is why we all recommend bringing a zip lock bag, containing all your valuables and electronics into the shower stall with you. Never be separated from the impossible, or really hard to replace items.
This is also, anecdotally, why some folks state that it is possible to do the Camino with the clothes on your back and lots of money...
I hope this helps.