The nation’s largest auto insurer has hit some speed bumps. State Farm swung to an underwriting loss in its auto division last year, as premiums fell and incurred claims rose. Its overall annual profit slipped 36.4% from 2018, to $5.6 billion. The 98-year-old Illinois-based company still brought in $79.4 billion in revenue, down 2.9%, and kept its Fortune 500 rank steady. But it now faces a new slowdown from the lockdowns that have kept Americans off the road this spring. In April, as auto insurers widely announced pandemic-related refunds, State Farm said it would return $2 billion in auto-insurance premiums through customer credits.