You do seem to be obsessed with character-separated data in columns - which is bad practice by the way.
Based on the other questions you have been posting this is about performance when using FOR XML PATH because it requires a
correlated sub-query i.e. this is the bit that is causing the issue
ff.Masked_ID=FFFFF.Masked_ID
As you have been advised previously - try putting that data into a temporary table so that you are not impacting the larger query e.g.
declare @MultiMaskDemo table (FamilyGroupText varchar(10), Masked_ID int)
insert into @MultiMaskDemo ( FamilyGroupText,Masked_ID) values
('A',1), ('B',1),('C',1),('D',2),('E',2),('F',3);
select F2.Masked_ID, FamilyGroup = STUFF(
(
SELECT '|' + CAST( ISNULL(REPLACE(FamilyGroupText,'|','/'),'NULL') AS NVARCHAR(50))
FROM @MultiMaskDEMO f1
WHERE f1.Masked_ID = F2.Masked_ID
FOR XML PATH ('')
),1,1,'')
INTO #temp
FROM @MultiMaskDemo F2
GROUP BY Masked_ID
You can then join that temporary table to your main query based on Masked_ID. When you put your joins back into this demo code you can change
INNER JOIN Parts.Nop_Part ptt WITH(NOLOCK) ON ptt.Masked_ID=ff.Masked_ID AND ptt.Masked_ID = FFFFF.Masked_ID
to be
INNER JOIN Parts.Nop_Part ptt WITH(NOLOCK) ON ptt.Masked_ID=ff.Masked_ID
- No need for two references to the outer query.
As an aside, I strongly advise you to stop using character-separated values in columns - create a many-to-one relationship table for storage and only generate the CSV when required (if at all)