This may sound like a fairly silly solution to air bubbles but check to see if
it has been coverslipped with duplicate or triplicate coverglass.  We have a
Hacker coverslipper and have had the same problem.  You can try to adjust the
pressure on the coverglass but usually doe not correct it.  The coverglass can
be notorious about sticking  together. The manufacture's solution to sticking
is to produce coverglass with tiny beads to prevent sticking together.   If you
watch as it is working you will see it happen.  A real problem and a waste of
coverglass and time.  One of the prices I guess we pay for automation.