We know Wade Davis was bad in 2019. He was second to last on the team in rWAR and worst among pitchers. But we also know that Davis will be on the team in 2020, so the question is why was he bad and can he fix it? Thomas Harding in this article discusses those questions.
As far as the why was he bad question, Harding mentions the possibility that Davis wasn’t fully healthy, although even Davis doesn’t think that was a reason. Harding points to a velocity decline of about 1 mph after suffering an oblique strain in May.