In #2506213: Update content entity changed timestamp on UI save we extended the EntityChangedInterface with the function setChangedTime and implemented it in the EntityChangedTrait.
All the entities in core which are implementing the interface now use the function from the trait and their own implementations have been removed.
From now on all contrib entites which are implementing the EntityChangedInterface and also using the EntityChangedTrait have to remove the setChangedTime implementation from the entity, if it was defined.
Entities implementing the EntityChangedInterface but not using the EntityChangedTrait have to implement their own setChangedTime function.