vzpkg update <CTID> command exits with empty output after installing Update 8.
# vzpkg update <CTID> #
Issue is recognized as an internal bug with ID #PSBM-30365.
Public fix will be included in one of the nearest updates.
Until hotfix is released you may use following command as a workaround:
# vzpkg update CTID -p '*'
It will work the same way
vzpkg update <CTID> command.