if is very thin hairline "cracks" then dont worry about it too much
i think the theory is to create a hard outside layer so sounds like you are doing a thorough job.
It has also been discussed how oil helps soften the top layer of wood and helps the fibres bond together.
IF the bat is lightly oiled and there are a few thin cracks i might think of giving it a touch of oil, leave it over night and continue knocking then if you think it needs a bit more.
If the cracks have any width then i would consider contacting manufacturer. You could put pictures up