We have the same issue. Upgraded today and now our script doesn't work.
Will try the suggestion noted here
edit: try to change our script to but still no luck
#echo %DATE% %TIME% > "C:\Program Files\VieCuri\scripts\postsync.txt"
echo N | gpupdate /force
shutdown -r -f -t 00
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Provisioning error occurred for Machine CSICTEST1-0003: Instant Clone agent initialization failed
Instant Clone agent initialization state error (19): Failed to execute postsync script