After a few days of digging and a few questions to ChatGPT I got the right answer. The problem was in synchtonizxation. Here is the code to fix it:

public async Task<ArticleElastic> SaveAsync(ArticleElastic entity)
{
    await _elasticsearchClient.CreateAsync(entity, i => i.Id(entity.Id).Index(IndexName).Refresh(Refresh.True));
    return entity;
}