Error migrating calendar items, "At least one property failed validation., Can't save invalid object Object Violation. Invalid property = [Calc:StartTime] StartTime." (4344026)

When migrating calendar items, in rare circumstances, you may experience the following error:

At least one property failed validation., Can't save invalid object Object Violation. Invalid property = [Calc:StartTime] StartTime. Invalid data for that property = Property: [Calc:StartTime] StartTime, PropertyErrorCode: NotFound, PropertyErrorDescription: .. Constraint violated = Property [Calc:StartTime] StartTime is required and must contain a valid DateTime value...