If I understand correctly, only one of Einstein's papers was ever subjected to peer review. He didn't like it. [0]
There are some situations where peer review has led to groupthink. The one that comes to mind is the amyloid hypothesis. [1]
[0] https://theconversation.com/hate-the-peer-review-process-ein...
[1] https://www.science.org/content/article/potential-fabricatio...