Batch problems follow the pattern of installation.
Batches are groups of shingles made during the same production run from the same batch of asphalt. Batch problems are problems caused by installing shingles from different batches on the same roof. Shingles from different batches can weather at different rates. Over time, fairly small differences in shingle thickness or in the composition of the asphalt mix can affect the rate at which shingles deteriorate.
The distinguishing characteristic indicating batch problems is the pattern of deterioration. It follows the stairstep/offset pattern of installation. Batch problems typically become apparent as shingles approach the ends of their warranty period.
Batch problems are natural aging, not a manufacturing defect. Whether the roof is at or near the end of its useful life depends on what percentage of the shingles are bad and how bad the good ones are.