Repairs to Granite Countertop

The granite apron cut tiles fell off and I was called out to replace them.  There are many possible reasons why these tiles fell off.  The mortar underneath the skirt cuts was soft and degraded easily by just pushing on it with a chisel.  This was either defective mortar or mortar that had too much moisture in it when it was installed.  The apron cuts should have been dried off completely after being cut on the wet saw; these cuts could have contained too much moisture when originally installed.  And lastly, the thinset glue used to apply the tile could have been old, too dry, or defective as well.