elasticsearch从6.5升级7.4后查询使用"fuzziness": "AUTO"，高亮无返回结果

elasticsearch集群从6.5升级到7.4以后，在6.5上正常的请求，在7.4上高亮字段使用unified highlighter 无返回结果(返回的结果中就没有"highlight": {}字段，不是该字段为空)，elasticsearch后台也无错误日志。
查询请求类似：
{"from":0,"size":3,"query":
{"bool":{
"should":[
{
"match":{
"field":{
"query":"xxx",
"operator":"AND",
"fuzziness":"AUTO",
"prefix_length":0,
"max_expansions":50,
"fuzzy_transpositions":true,
"lenient":false,
"zero_terms_query":"NONE",
"auto_generate_synonyms_phrase_query":true,
"boost":3
}
}
}
]
}},"explain":false,"_source":{"includes":[],"excludes":[]},"highlight":{"pre_tags":["<em>"],"post_tags":["</em>"],"fragment_size":150,"number_of_fragments":0,"require_field_match":false,"fields":{"xxx":{}}}}
 
换用fvh或者去掉"fuzziness":"AUTO"都有高亮结果，但是unified highlighter和"fuzziness":"AUTO"组合则不行