The joins are all messed up. It runs forever because it's generating a partial cartesian product. Try this instead:
SELECT
u.Useraccount_First_Name,
u.Useraccount_Last_Name,
x.*
FROM Application_Useraccounts u -- "driving" table is now correct
CROSS APPLY (
SELECT
Useraccount_Status_DateTime = MAX(Useraccount_Status_DateTime),
Duration_UserLogin = MAX(CASE WHEN Useraccount_Status_ID = 1 THEN Useraccount_Status_Duration END),
Duration_PauzeKort = MAX(CASE WHEN Useraccount_Status_ID = 2 THEN Useraccount_Status_Duration END),
Duration_PauzeLang = MAX(CASE WHEN Useraccount_Status_ID = 3 THEN Useraccount_Status_Duration END),
Duration_Beschikbaar = MAX(CASE WHEN Useraccount_Status_ID = 4 THEN Useraccount_Status_Duration END),
Duration_Storing = MAX(CASE WHEN Useraccount_Status_ID = 9 THEN Useraccount_Status_Duration END),
Duration_Werkoverleg = MAX(CASE WHEN Useraccount_Status_ID = 10 THEN Useraccount_Status_Duration END),
Duration_NietBeschikbaar = MAX(CASE WHEN Useraccount_Status_ID = 11 THEN Useraccount_Status_Duration END),
Duration_Overdracht = MAX(CASE WHEN Useraccount_Status_ID = 12 THEN Useraccount_Status_Duration END),
Duration_Beheer = MAX(CASE WHEN Useraccount_Status_ID = 13 THEN Useraccount_Status_Duration END)
FROM Application_Useraccounts_Status s -- "child" table
WHERE s.Useraccount_ID = u.Useraccount_ID -- outer reference
AND Useraccount_Status_ID IN (1,2,3,4,9,10,11,12,13)
) x
For fast, accurate and documented assistance in answering your questions, please read this article.
Understanding and using APPLY, (I) and (II) Paul White
Hidden RBAR: Triangular Joins / The "Numbers" or "Tally" Table: What it is and how it replaces a loop Jeff Moden