During the hike, you found that the compass needle began to behave uneasily, showing one direction or the other. Why could this happen?

If during the hike, passing through some area, the compass needle stopped pointing in one specific direction, then, most likely, there are large deposits of iron in this area, located at a shallow depth from the surface of the earth. Large deposits of iron are capable of forming a magnetic field strong enough to interfere with the stable operation of a compass or any other electronic equipment.