Usually this is caused by old "orphan" batches lying around in the data directory from improper backup/restore procedures. When Ledger goes to create the new batch, it sees the old one and skips the batch number. Ledger batches are named "GLnnnnnI.dat" where nnnnn is the number of the batch. Check you data directory to see if there are any of these files with old dates and move them into another subdirectory.
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Andrew Bates