The components of any borg ship may or may not be connected directly to the control of the hive mind at any given time. They are assimilated from other vessels which may not be immediately compatible, and battle damage or maintenance could disconnect sections.
This isn't a problem though as the borg still control them through the hivemind, just using one or more drones as a relay as the most efficient path available. Any direct connection can just be considered a redundant backup in fact.
EDIT: As per the request for an example. The most recently seen would be from Picard S01E08 where
Seven of Nine plugs in and controls the start up of a Borg cube