I assume that the organ in question has vacuum for control and uses
pairs of unit valve blocks tubed together for lock and cancel
functions.  If this is the case, three bleeds (one from each unit valve
block) working into a single tracker bar hole will usually not work.

A suggestion would be to tube a new unit valve block (maybe your organ
has a spare valve block location on the relay board?) to the cancel
hole on the tracker bar.  Make a pouch block like those used for
membrane registers, but with only one large pouch on it.  This should
connect to the output hole of the new unit valve block used for the
cancel function.

The pouch should be made with a single large hole in the center to
atmosphere and the others around it tubed to the "off" unit block for
each pair of unit blocks.  The coated leather membrane would seal the
"off" tubes from atmosphere and the large hole would adequately vent
each one of them when pulled away by vacuum when the cancel hole
appears.

This cured the same problem I once had when building a lock-and-cancel
mechanism for a piano.

Dave Vincent