The product version job collection was modified enumeration operation may not execute – sometimes we may get this error from the SharePoint server that “Product Version Job: Collection was modified; enumeration operation may not execute ((Correlation=0b9de10e-4bb7-4010-ab62-e91d5375e0ac)”, and in the ULS log we will get the below entry: “at System.Collections.Generic.List`1.Enumerator.MoveNextRare() at Microsoft.SharePoint.Upgrade.SPUpgradeSession.NeedsUpgrade(Object o, Boolean bRecurse) at