401 unauthorized response only for a single report when using report pages REST API

Cross posting in case I placed this in the wrong forum. 

We have a customer who is getting a 401 unauthorized only for the report pages API using a service principal. 

They are successfully able to run these APIs without any issue: 

https://learn.microsoft.com/en-us/rest/api/power-bi/groups/get-groups

https://learn.microsoft.com/en-us/rest/api/power-bi/reports/get-reports-in-group

and even https://learn.microsoft.com/en-us/rest/api/power-bi/reports/get-pages-in-group for one report, but this last API doesn't work for one of the other reports, and the error is the following:

HTTP error code 401 Unauthorized. 
 {
  "error" : {
    "code" : "PowerBINotAuthorizedException",
    "pbi.error" : {
      "code" : "PowerBINotAuthorizedException",
      "parameters" : { },
      "details" : [ ],
      "exceptionCulprit" : 1
    }
  }
}

I was not aware of any specific permissions which applies to report pages. Why would we get this error for one particular report? Are there circumstances where we can't query the pages for some reports due to authorization?