Peeling is caused by sealcoating not bonding to oil spots or any other surface contaminants like dirt, grease, etc. or oxidized pavements. Prior to sealcoating application, the pavement surface shall be thoroughly cleaned, oil spots be treated with an oil spot primer. And oxidized surface be primed either with a specialty primer or a thin coat of the sealer or a tack coat.
Peeling and dis-bonding, may also be caused by freezing temperatures during the final cure process, before the film was fully cured. Freezing temperatures will shatter the sealcoating bonds from the bottom layers of the sealer film.
Deposit of tree sap in the pavement profile. The failure is seen as the flaking of the sealer.
Sealcoating over a very hard coating, e.g. Gilsonite-based. The failure appears as chipping because the top coat does not bond and flex with the bottom coat.