Search results behavior with boosts are different from 6.8 to 7.1

[Yann_Lair]

Hi,

We are currently doing the ground work to migrate from ES 6.8 to latest (which is 7.1 on AWS server side). We have built a new set of environment to be able to assess the impact of that change and we are seeing search results differences that we cannot explain. Note: using the exact same code to build the index and do the search with the exact same query.

The problems is that the explanation gives us very different result, even though the total roughly come to similar points. The weirdest of those is the boost. When we give a boost of 15 for a particular field, it comes back in the explanation with a value of 15 in v6 (as expected) and 33 in v7! We have no idea what is triggering that changes.

Any chance to get an explanation on how the boost values aren't consistent anymore between query and explanation in v7?
I've put a simplified version of query and the 2 outcomes below.

Thanks you very much.

Yann.

Query has:

GET /logodesigns2/_search
{ 
   "explain":true,
   "from":0,
   "track_total_hits": true,
   "query":{ 
      "bool":{ 
         "should":[ 
            { 
               "term":{ 
                  "isOwned":{ 
                     "value":true,
                     "boost":15.0
                  }
               }
            }
         ]
      }
   },
   "size":32
}

Here's the explanation for v6

                {
                  "value": 6.758246,
                  "description": "weight(isOwned:T in 2242) [PerFieldSimilarity], result of:",
                  "details": [
                    {
                      "value": 6.758246,
                      "description": "score(doc=2242,freq=1.0 = termFreq=1.0\n), product of:",
                      "details": [
                        {
                          "value": 15,
                          "description": "boost",
                          "details": []
                        }
                      ]
                    }
                  ]
                },

Here's the explanation for v7

                {
                  "value" : 6.391614,
                  "description" : "weight(isOwned:T in 18403) [PerFieldSimilarity], result of:",
                  "details" : [
                    {
                      "value" : 6.391614,
                      "description" : "score(freq=1.0), product of:",
                      "details" : [
                        {
                          "value" : 33.0,
                          "description" : "boost",
                          "details" : [ ]
                        }
                  ]
                },

[Yann_Lair]

Found some sort of explanation here:
https://issues.apache.org/jira/browse/LUCENE-8563

Is there anyone else that can confirm that's the explanation?