I have had the same thing happen a number of years ago on staves I thought were dry, the backs had been shellacked, I chased a ring to start a bow, leave it for a few days and come back to drying checks.
All my wood has been cut for at least 10 years ago now, none was stored with the bark and sapwood on so I don't have that problem anymore. I still check it with a moisture meter to be sure it is completely dry before I leave the back unsealed.