azure – CustomScriptExtension failed with “Operation is not valid due to the current state of the object”

I’m using CustomScriptExtension with ManagedIentity and sometimes it fails with

"Failed to download all specified files. Exiting. Error Message: Operation is not valid due to the current state of
the object."rnrnMore information on troubleshooting is available at
https://aka.ms/VMExtensionCSEWindowsTroubleshoot "

What does this error really mean?