Why is the grass coming through my floors?

Hello fellow vault dwellers!

Yesterday, out of nowhere, grass appeared through the floor in my main camp. I didn't change anything in the building, just changed the lobby and suddenly there was grass everywhere (see photo). Now the grass suddenly appears in every server and even if I remove the floor and put it back, the grass stays there!

Does anyone know why this suddenly happened out of nowhere and how I can remove it again? Changing the floor doesn’t affect it! Thanks in advance…