Import is no longer possible after the upgrade. A restart of Tomcat was also unsuccessful as mentioned in the article below.
Release : 12.3
Component : AUTOMATION ENGINE
Compared the debug logs generated in customer environment with my test environment.
2021-05-28 17:00:52,971 http-nio-8080-exec-10 [DEBUG] AUTOMICT:0/MATOEPKE/BITS 0 0000000013149022 [.framework.commons.upload.ExtendedUpload] - Upload of file export_NEU.xml received
2021-05-28 17:00:52,979 http-nio-8080-exec-10 [ERROR] AUTOMICT:0/MATOEPKE/BITS 0 0000000013149022 [com.uc4.webui.common.errorhandling.Safe] - Invocation of method uploadFailed in com.uc4.ecc.framework.commons.upload.ExtendedUpload$3 failed.
The failure is happening at the upload of the file.
A similar debug if the problem did not happen should be like this,
Test environment log
2021-06-04 19:48:09,229 http-nio-8080-exec-6 [DEBUG] AUTOMIC:100/AE/AE 0 0000000001248009 [.framework.commons.upload.ExtendedUpload] - Upload of file export_NEU (1).xml received
2021-06-04 19:48:09,229 http-nio-8080-exec-6 [DEBUG] AUTOMIC:100/AE/AE 0 0000000001248009 [ework.commons.upload.ExtendedUploadField] - Upload finished: UploadResult [filename=export_NEU (1).xml, mimeType=text/xml, temporaryFile=C:\Automic\External.Resources\apache-tomcat-9.0.19\temp\ecc-fileupload-9068497694476475638.tmp]
There is a problem in uploading the file to the temp location. So it could have been due to a permission issue in the AWI server especially with the user the tomcat is running as.
After using another user to start tomcat in windows and now it works fine.