Why is Concatenation of 2 nvarchar(max) values truncating?

I'm using a cursor to concatenate all the values of the OriginalComments column into one variable called @Comments.  Both are declared as nvarchar(max).  Why does the line where concatenation occurs result in an empty string?

Declare @Comments nvarchar(max)
Declare @Question nvarchar(max)
Declare @DisplayOrder nvarchar(max)
Declare @OriginalComments nvarchar(max)
 
OPEN Comments_Cursor
FETCH NEXT FROM Comments_Cursor INTO @Question, @DisplayOrder, @OriginalComments
 
WHILE @@FETCH_STATUS = 0
BEGIN
	Select @Comments = rtrim(@Comments) + rtrim(@OriginalComments) + '; '
	Print @OriginalComments
	Print rtrim(@Comments)
FETCH NEXT FROM Comments_Cursor INTO @Question, @DisplayOrder, @OriginalComments
END
CLOSE Comments_Cursor
DEALLOCATE Comments_Cursor
 
Print @Comments

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