Can not add highlight option of fragments number

I have a simple elasticsearch-dsl-py code. Everything is fine, even tags, except number_of_fragments. Response continuing giving multiply highlights for single word.

def name_autocomplete(q):
    multi_match = MultiMatch(query=q, fields=ngram_fields, fuzziness='AUTO', tie_breaker=1)
    s = s.query(multi_match)[0:5] \
         .highlight_options(pre_tags='<b>', post_tags='</b>',
                            number_of_fragments=1,  # This is not working
                            order='score') \
         .highlight('name.ngram') \
         .execute()
    response_dict = s.to_dict()
    return Response(response_dict)

What am I doing wrong?

ADDED:

Analyzer:

edge_ngram_completion = analyzer(
    "edge_ngram_completion",
    tokenizer=tokenizer('trigram', 'nGram', min_gram=3, max_gram=4),
    filter=["lowercase"]
)

Document:

class TerminalDocument(Document):
    """Document Elasticsearch document."""
    id = fields.IntegerField(attr='id')
    name = fields.TextField(
        fields={
            'suggest': fields.TextField(analyzer=ascii_fold),
            'ngram': fields.TextField(analyzer=edge_ngram_completion)
        }
    )

Example of hidhlighting for foobar:

"<b>foo</b>something<b>bar</b>"