Schrodinger Code - XLOOKUP

[Duncaroos]

I have a sheet where I have a custom formula that is used for a graphical schedule on an Output sheet in excel. The function outputs the Date that is closest to the "MilestoneDate" input, but also places a physical marker/shape in the correct location on the sheet containing the schedule. I am having an issue with the line highlighted below in bold text (ONLY when there is a code break before this line); I get Excel VBA Error 424 "Object Required". If I do not have any breaks before this line, the function works fine.

I only can get XLOOKUP to work when MilestoneDate and TempOut are set as RANGE data type. Graph_Dates shows its output like this Graph_Dates Snapshot, which maybe(?) is part of the problem, but I don't get why if I do not watch before this problematic line the function behaves normally. I put it I have made a grave mistake somewhere that I am not seeing.

Function Milestone(WBS As String, MilestoneDate As Range, ShowMarker As Range, TaskID As Long, Grph_Dates As Range, Grph_UIDs As Range, Watch_TaskColors As Range) As Variant

    Milestone = ""  'Default Output
   
    'Define Task Table (For Marker Generation)
        Dim TTbl As ListObject
        Dim Ind_Tsk As Long
       
        Set TTbl = DataSheet.ListObjects("DataTable_Tasks")
        Ind_Tsk = TTbl.ListColumns("Task").Index
   
    'Define Variables for Date & Cell Targeting
        Dim TempOut As Range                                       'Temporary storage of function output
        Dim UID As String                                                 'Unique Identifer for Row search
        Dim col As Long                                                    'column # for shape location
        Dim row As Long                                                   'row # for shape location
        Dim Trgt As Range                                                 'Target Cell for shape location
   
    'Do Stuff
        On Error GoTo skip
            If WBS <> "" And MilestoneDate <> "" And ShowMarker.Value = True Then
               
                With WorksheetFunction
                    Set TempOut = .XLookup(MilestoneDate, Grph_Dates, Grph_Dates, , 1)                      'Find relevant date on graph for location {{{Excel VBA Error 424 when in debug}}}
                   
                    If Not (IsEmpty(TempOut)) And Err = 0 Then                                              'If no error (date found) - Find Cell Address
                        Milestone = TempOut
                       
                        'Unique ID for finding correct Graph Row to Assign Marker:
                        UID = WBS & "_" & .XLookup(TaskID, _
                                                   TTbl.ListColumns(1).DataBodyRange, _
                                                   TTbl.ListColumns(Ind_Tsk).DataBodyRange, _
                                                   , 0)
                       
                        col = .Match(TempOut, Grph_Dates, 0) + 8                                    'Cell Column #
                        row = .Match(UID, Grph_UIDs, 0) + 3                                             'Cell Row #
                        Set Trgt = OutputSheet.Cells(row, col)                                           'Set Target Cell
   
                        'Call DrawMilestone(WBS, TaskID, ShowMarker, Trgt, TTbl)
                       
                    Else
                   
                        GoTo DMS
                       
                    End If
                   
                End With
               
            Else
           
DMS:            If WBS <> "" Then Call DeleteMilestone(WBS, ShowMarker, TTbl)
               
            End If

skip:
    Call InvalidMilestone
   
    'Call EnableWorkbook

I do have some global variables at the top of the module:

Option Explicit
Global TempCalcCode As Long

TIA