The phrase "undeserved reputation" means that someone has a reputation or a perception about them that they did not earn or deserve based on their actions or behavior. Full definition
«And if he doesn't, the danger is that he will compound a probably undeserved reputation for being indecisive.» (theguardian.com)
But watch it again, and you'll see how undeserved that reputation is. (timeout.com)
We should welcome the March for Science as it sets out to destroy the academy's undeserved reputation for neutrality and to reveal science for what it has always been. (firstthings.com)