What is this in the soil?

I have a problem with my plants. I noticed something in the soil (please see attached pictures). I want to know what these things are, why they appear, and how i can avoid them?

Thank you.

Seems some liverwort on the top picture. It is harmless, but does not look good.
However the plant on the top picture does not look good either. Possibly there is/was something wrong with the plant and therefore liverwort takes over.

I would advise to try a new plant pod.