African Butterfly Cichilds

Do you mean this fish? And do you have a male and female? And do you have any decor that could be classed as a flat rock?
According to the link, these fish lay eggs on flat rocks or other decor and dig pits in the substrate near the breeding site. Once the eggs have hatched, the fry are moved to these pits.

This could be what you are seeing. Even with just one fish, the urge to do this could be strong enough without a mate or eggs.



Of course it could also be something completely different.......