As a published novelist and fiction writing coach, I've come to understand that there are two main causes of Writer’s Block.
Each plagues writers in different ways and at different times, whatever the individual writer's experience.
Far and away, the biggest roadblock to fiction writing is The Inner Critic, that very personal fear monger dwelling within you. It’s almost as if there’s a radio in your head that has only one DJ, the Inner Critic. While you can’t kill your Inner Critic, you can defang it.
The second reason for Writer’s Block is that you genuinely don’t know where to go next with your characters or your plot, or both.
Two of my favorite techniques to help guide students through this block are Using Images As A Bridge Into The Imagination, and asking and answering What If questions.