Unhappily, they have become a reality of the Camino, as indeed for many other places in the world (from New York to Sydney…)! This is not a reason to make an obsession of the issue.
Pay attention to the rules generally recommended : if possible leave your backpack outside of the bedroom; enclose it in a large trash sack for the night; inspect the sheets before going to bed; shake your sleeping bag vigorously (outside of the hostel!) every morning before returning it to your backpack…
If you have encountered bedbugs, put your backpack in a freezer for three days on returning home. Know that the commercial products are not always very effective and are only repellent. But,this is not so bad !