Suspended cards

I keep getting cards marked as leached and suspended. What causes that?

This is the default behaviour of Anki (see the chapter on leeches of the manual).

You can change Anki’s behaviour regarding leeches in the deck options (cog-symbol on the right of the deck) under “Leeches”.
I usually set it to “only mark” so I can decide what to do with them on my own.