Last year, Cease was almost laughably unlucky when he pitched. His defense betrayed him pretty much every start, multiple times. He was getting Quintana'd left and right. The difference between his ERA and RA was massive because of all the errors.
In addition, his biggest "problem" heading into this season was not pitching deep enough into games, but can you blame him when he had to throw an extra 20-30 pitches every night due to errors?