In total, I counted 10 markers on the map - 8 on the surface, 2 in the dungeon.
I had to approach each one until a message appeared - 2 steps back, i.e., 2 markers back. If you're on the right path, the marker displays a message in a frame; if the marker is incorrect (you're not approaching in the correct sequence), it displays some nonsense. When the message is in a frame, it's a description of what the next one should be, and so on. In principle, it turned out to be very simple, it just took some time. Naturally, everyone will have their own location where to dig - this was also in Heroes 3; the Grail is buried in a different place each time...:D So, there are no bugs; try all the markers and remember there are 10 of them.