> I confronted my manager, they accepted their mistake, took full responsibility and apologized for what had happened. They stated that my current performance was strong and I had nothing to worry about.

In my opinion, that wasn't a mistake. The manager was telling the employee that he was doing great for a long time and then suddenly told him that he wasn't.

What does "took full responsibility" mean in this case? The manager will face no consequences at all and the apology sounds a lot like a politician's apology.