Shiser said: Possibly when your hand is already full? Like if Deathsprout is being cast from somewhere besides your hand?
I can concur that I have had many instances where deathsprout did not fetch a land.
What land were you trying to fetch?
I noticed that today also
I hadn't noticed this with Deathsprout, but I did notice this at least once last week running District Guide in a Vivien build with 3 Gates.
I wasn't sure what caused it but the 40-card deck instance issue, not appending another deck to my library, seems consistent with the behavior.