Morally undefeated, we know.2012 he was suffering from tendinitis in his knee and subsequently withdrew from the Olympics, USO and the entire rest of the season.
2013 was a legitimately bad loss. He played the tiebreaks poorly. It happens a few times in a career.
2014 Rafa played a great match, 44 winners and 18 UE. Kyrgios simply played out of his mind to the tune of 70 winners and servebotted out the tiebreaks.
2015 he was playing the worst tennis of his career.
2016 he missed the tournament.
2017 he played an amazing match and lost an epic battle. He actually won 7 more points than Mueller. 77 winners, 17 UE. However, just 2 of 16 BP converted.
There you have it. Rafa struggling at Wimbledon is generally a misnomer and if you look behind the curtain, you will notice that he has actually been unlucky at the tournament and his prowess on grass has never wavered. Of course most people don't like to be confronted with the truth, but there it is.