When was the last time a guard left his post at the tomb of the unknown soldier?

The last time a guard left his post at the Tomb of the Unknown Soldier in Arlington National Cemetery was on March 20, 2020. The guard was temporarily relieved due to the COVID-19 pandemic, and the tomb was closed to the public for a brief period. However, the Sentinels of the Tomb resumed their duties in June 2020, maintaining a 24/7 vigil.