Thanks for your reply,
I did some digging and i found a bug report on jira
https://alfresco.atlassian.net/browse/MNT-22988?focusedCommentId=1120337
see also for more explanation : https://alfresco.atlassian.net/browse/MNT-22385?focusedCommentId=1087195
It seams that "this is not a bug"... but an expected behavour related to permissions check.
The "solution" i found is to use IN_TREE in replacement of IN_FOLDER to force the query to be executed on SOLR.
EDIT: I found an other solution, it's possible to increase the max permissions check number in the query body with the property "limits".
"query": {
"query": "SELECT * FROM cmis:document WHERE IN_FOLDER('fc896c39-b13b-493a-bdeb-9152d8495dd0')",
"language": "cmis"
},
"fields": [
"id"
],
"paging": {
"maxItems": 1,
"skipCount": 0
},
"limits": {
"permissionEvaluationCount": 10000
}