Edition: Data Interoperability, Fixed OEM License
Version: FME(R) 2025.0.0.0 (20250228 - Build 25208 - WIN64)
OS Locale Name: en_US
OS Encoding: windows-1252
Process Encoding: UTF-8
FME API version: 4.0 20240722
Home Folder: C:\Program Files\ArcGIS\Data Interoperability for ArcGIS Pro\
Operating System: Microsoft Windows 11 64-bit (Build 26100)

For clarity, I am working with FME Workbench provided by Esri in both the Data Interoperability extension for Pro - and Server.  The server situation is worse at this point, so to start, I am just going to address the problems that I am seeing on my laptop.

I am calling a number of different API endpoints with an HTTPCaller, manipulating the data, and then pushing (updating) the data in an ArcGIS Online (AGOL) Feature Service.  When I was building this workflow, I was successful in writing changes to the Feature Service.  I can step through transformers, check the cached data and then click on the ‘Run To This” to run the cached data from the previous transformer through either the “ArcGIS Online (AGOL) Feature Service Writer” or the “FeatureWriter”.  The Feature Service will get the updates.

IF I use “Rerun the Entire Workspace”, no features write to the Feature Service.

2025-08-07 15:35:09|   9.4|  0.0|WARN  |ArcGIS Online Feature Service Writer: 'updateResults' error for a feature in 'PowerOutage'. The error code from the server was '1000' and the message was: 'Conversion failed when converting date and/or time from character string.'

I have also noted this twice in the logfile:

2025-08-07 15:34:53|   0.3|  0.0|WARN  |The current FME process locale has been changed from 'English_United States.utf8' to 'en-US' and FME has restored it back to 'English_United States.utf8'. It is undefined behavior to call 'setlocale()' in plugin code and doing so may cause unexpected errors

I have gone back through and checked that all field types to the ONE datetime field are all set to “datetime”.  I have made sure that the datetime format is FEM datetime (by reformatting when necessary) - (although, I have previously had success with other formats when sending to an AGOL FS).  I can run the individual writer and everything is fine, but as soon as I run the entire workspace, It throws the error.

Any pointers would be appreciated!
--Adam