sudden workflow error on very wf that was not changed at all

I have not changed this flow and it has run successfully for over a year in O365 environment. Now I am get a date string error.  I added a log and the two dates in the flow are populating properly, but it is still suspending.

Here is the error: 

RequestorId: 31400ede-35c9-73f5-0000-000000000000. Details: An unhandled exception occurred during the execution of the workflow instance. Exception details: System.FormatException: The string was not recognized as a valid DateTime. There is an unknown word starting at index 0. at System.DateTimeParse.Parse(String s, DateTimeFormatInfo dtfi, DateTimeStyles styles) at Microsoft.Activities.Expressions.ParseDate.Execute(CodeActivityContext context) at System.Activities.CodeActivity`1.InternalExecute(ActivityInstance instance, ActivityExecutor executor, BookmarkManager bookmarkManager) at System.Activities.Runtime.ActivityExecutor.ExecuteActivityWorkItem.ExecuteBody(ActivityExecutor executor, BookmarkManager bookmarkManager, Location resultLocation) Exception from activity ParseDate DynamicActivity<DateTime> Cast<DateTime,Object> BuildDictionary<String,Object> Subroutine<Guid> Sequence Action Set Sequence Flowchart wfRollOffTask.WorkflowXaml_079e21c7_e642_45ac_8688_de2bde33ea2d