In a dysfunctional situation (which, sad to say, it sounds like you could have), the first thing to go is trust. And when that happens, management statements are no longer believed. Ironically, the more you say about not planning layoffs, the more that can be taken as proof that layoffs could happen.
Similar with the scars from previous management and toxic employees. That history isn't quickly forgotten, even if the perpetrators are gone. That sort of abuse can be self-propagating: it becomes a learned behavior that turns victims into new abusers.
The good news is that you can recover, but it takes time and effort.