Error description:
After updating ArcGIS Enterprise from 11.3 to 11.5 and simultaneously updating ArcGIS Pro from 3.3.1 to 3.5.2, the behavior when creating feature layers in the ArcGIS Enterprise portal from Python (ArcGIS API for Python - arcgis 2.3.0 to 2.4.1.1) has changed at our system. The creation of a featurelayer in the portal datastore from a csv-File now takes more than 15 times longer than before.

System:
Clients: Win 11 Enterprise Client with ArcGIS Pro embedded Python Installation.
Servers: Federated ArcGIS Enterprise System: Portal Server, ArcGIS Server, DataStore Server (Postgresql) - all Win Server 2022 Standard

Process:
We use the ArcGIS API for Python to publish automatically data using Python to a feature layer in the Enterprise datastore. This worked perfectly and with a short execution time. After updating, the csv-file is still quickly published to the portal as before. But the part publishing the feature layer takes now 15 times longer than before.
Line of code that now takes so long:
self.feature_layer = self.feature_class.publish(
"type": "csv",
"locationType": "coordinates",
"latitudeFieldName": "lat",
"longitudeFieldName": "lon",
"dateFieldsTimeReference": {
"timeZone": "UTC",
"respectsDaylightSaving": True
}
})
The process has been running smoothly for many years and versions. The delivered files usually contain 2000-10000 features.
Since the desktop software/libraries were upgraded to ArcGIS Pro 3.5.2, the code remains executable, there is no error, just the loss of performance.

Things we already tried:
We talked with Esri Support, but found no solution so far, because the problem is not reproducible with the same data on their system.
The problem also exists with small datasets.
The problem also occurs when “dateFieldsTimeReference” is left out.
In some documentation, a name was also transferred during publishing. This was also tested and did not result in any changes.
We still have one client with ArcGIS Pro 3.3.1 with the ArcGIS API for Python 2.3.0: The whole process runs fast in 1 minute.
On our updated clients with ArcGIS Pro 3.5.2 with the ArcGIS API for Python 2.4.1.1: The whole process runs slow in 15 minutes.
On a updated client with ArcGIS Pro 3.5.2 from a conda environment with the old Libraries (ArcGIS API for Python 2.3.0): The whole process runs fast in 1 minute.
We put the debug level on the ArcGIS Server protocol to debug, but didn't found there any hints between publishing with 2.3.0 or 2.4.1.1 libraries. We know the position between two messages where the time got lost, but found no reasons so far:

<Msg time='2025-11-18T14:45:21,899' type='VERBOSE' code='20025' target='System/PublishingTools.GPServer' methodName='GPServerSync.Deactivate' machine='name.de' process='23240' thread='28404' user='username@DOMAIN' elapsed='0,00018' requestId='9dc7c5f9-93dd-457b-bcc2-a379da30304b'>GPServerSync.Deactivate</Msg>
  <Msg time='2025-11-18T15:02:17,144' type='DEBUG' code='80020' target='System/PublishingTools.GPServer' methodName='RasterStoreHelper' machine='name.de' process='23240' thread='28404' user='username@DOMAIN' requestId='25218a3b-f25b-4ef9-a548-6b593f7be471'>username@DOMAIN</Msg> 

We checked the Browser Development Tools Console and Network tab, but didn't find hints between publishing with 2.3.0 or 2.4.1.1 libraries.
We checked certificates and let our virus scan service providing department executing checks while code war running.

If you know the problem and you know solutions or you have any ideas what else to check, please let us know.