Alternatively, at the moment, we could turn around and ask, "what's wrong with"? Alcantara, Nola, Wheeler, Manoah, etc...
Every year, you have aces who start the season slow. Burnes happens to be one of those pitchers this year.
The Arizona start and the last three innings of yesterday's start show it's still there. As he said post-game yesterday, the pec thing kind of threw off his routine this week and he's looking forward to getting back to normal this week.