Auto Row Highlighting Works on Only One Sheet

[Snake Eyes]

Greetings,
I've applied the code below to two (2) sheets in the same workbook. These two worksheets are identically configured when it comes to columns, formatting and macros. The only difference is the data/values in the rows/cells.

The code highlights a row by bolding and underlining text when the row is selected. The code works in Sheet1 but not in Sheet2.
Can someone help me understand why this is?

Private Sub Worksheet_SelectionChange(ByVal Target As Range)
' Sets the selected row text to bold and underline
    With ThisWorkbook.Names("HighlightRow")
.Name = "HighlightRow"
.RefersToR1C1 = "=" & ActiveCell.Row
End With
End Sub

Here is the formatting for the first sheet that works...

Here it is for the 2nd sheet that does not work...

 

[Snake Eyes]

I should clarify that my first worksheet (where the formatting works) is Excels "Sheet 3" and my 2nd worksheet (where is does not work) is Excels "Sheet 8".

 

[Snake Eyes]

I've discovered that when these two sheets are in the same workbook, the auto formatting will only work on one of the worksheets. It will only work on both sheets when they are separated into two different workbooks.
Any assistance in identifying the reason for this would be greatly appreciated.