That is called a run.  It's either a gasket problem or a crack in
a board.  Look for a board that has channels through it to the pouches.
This would be like a pouch board that has all the pouches in two or
three rows of pouches on it.  In the case of such a board, you will have
to remove the pouches involved and pour shellac through the channels.

When I redo one of these boards I pour shellac through the whole thing
before I cover pouches.  I have a time or two had to remove all the
_new_ pouches to do this because I had several runs or multi ciphers.

Also, if you tape up all the holes to the pouches you may open one and
blow into it and notice that when you pressurize one pouch, then the
two or three on each side slowly go up.  This tells you that all the
channels are open to wood pores.  It is just one more step before they
all open enough to call a crack as wood dries further.  This also
drastically slows the player action response even if it does not cause
a run.

So you may want to redo that pouch board if this is your problem.
Once poured with shellac I have never had any runs from pouch to pouch.
Almost all of these boards nowadays have this problem so never do
another without sealing all the channels.  Also, paint the inside of
the pouch well with shellac while you are at it.  You have to remove
the bleeds before you pour and replace them when dry, by the way.

D.L. Bullock
www.dougbullock.ws