I’m sorry I don’t have specific examples because it’s been a while, but IIRC generally the issues came from trying to mix compile-time dynamism with runtime dynamism. Things like depending on methods that made traits non-object-safe and so on.

I think it can be quite confusing initially how traits are both the unit of compile-time generics AND can be used for dynamic dispatch at runtime, given that there are separate rules about what can be used in which context.