Hi @abm ,
I ran the folowing sorting:
First: cr438_einddatum_sort desc, cr438_einddatum desc, cr438_startdatum desc
Second: cr438_einddatum_sort asc, cr438_einddatum desc, cr438_startdatum desc
cr438_einddatum_sort contains a date in the future if enddate is empty
cr438_einddatum contains real enddate. This is an optional field, since if it is actual assignment this field is empty.
cr438_startdatum contains real startdate. This is a mandatory field.
Both runs result in same order:

Later in the flow, the empty enddate is filled by a string "heden" (dutch for now).
This is the content of the data in both situations:
{
"statusCode": 200,
"headers": {
"Pragma": "no-cache",
"Transfer-Encoding": "chunked",
"Vary": "Accept-Encoding",
"x-ms-request-id": "0cafd47f-896c-4f4b-84b1-ac8cafd256d4",
"Strict-Transport-Security": "max-age=31536000; includeSubDomains",
"X-Content-Type-Options": "nosniff",
"X-Frame-Options": "DENY",
"Cache-Control": "no-store, no-cache",
"Set-Cookie": "",
"Timing-Allow-Origin": "*",
"x-ms-apihub-cached-response": "true",
"Date": "Mon, 06 Sep 2021 09:27:24 GMT",
"Content-Type": "application/json; charset=utf-8; odata.metadata=minimal",
"Expires": "-1",
"Content-Length": "87698"
},
"body": {
"@odata.context": "",
"value": [
{
"cr438_startdatum": "2011-12-01",
"cr438_einddatum": "2020-12-31",
"cr438_einddatum_sort": null,
},
{
"cr438_startdatum": "2019-04-01",
"cr438_einddatum": "2020-04-30",
"cr438_einddatum_sort": null,
},
{....
},
{
"cr438_startdatum": "2018-05-01",
"cr438_einddatum": null,
"cr438_einddatum_sort": "2031-09-06T09:27:24Z",
},
{
"cr438_startdatum": "2015-07-01",
"cr438_einddatum": null,
"cr438_einddatum_sort": "2031-09-06T09:27:24Z",
}
]
}
}
So null will always be on top over the filled cr438_einddatum_sort. No matter if it is descending or ascending. And I was not able to fill cr438_einddatum_sort with the same date as the cr438_einddatum if it was filled. Probably due to the fact that cr438_einddatum is a date only field and Dataverse does not allow date copying in calculated fields if it is date only.
Any solution?