2021.R1 Hardening - ROF when loading Manage Events Page

Description On JAT, the events page is throwing a Requested Operation Failed on Page load for every store.

The following error appears on Elmah:

"Invalid Operation" The sequence contains no matching element
System.InvalidOperationException: Sequence contains no matching element
at System.Linq.Enumerable.Single[TSource](IEnumerable`1 source, Func`2 predicate)
at Mx.Administration.Services.QueryServices.PeriodDetailQueryService.GetClosedDaysForWeekDateRange(GetClosedDaysForWeekDateRangeRequest request)
at Mx.Web.UI.Areas.Core.Api.EntityController.GetClosedDays(Int64 entityId, DateTime startDate, DateTime endDate)
at lambda_method(Closure , Object , Object[] )

To Reproduce:
Navigate to JAT Mobile
Navigate to Forecast->Manage Events

Results : ROF on page with red toast message.
Expected : No ROF