SQL CTE of a UNION kills performance

7.3 TR4, latest cume, DB group 10, Power 9.

I'm trying to suss out the performance issues in a very complex view,
and Visual Explain pointe me to this piece. 4 tables, UNIONed together
as a CTE. VE tells me that the UDFs are the culprit, but that makes no
sense as the exact same UDFs run in .001 over the exact same tables when
I run the 4 UNIONs alone.

This runs in milliseconds:

SELECT 'SOC' FILESOURCE, SOC.LOCNO LOCNO, SOC.SOCSEC SOCSEC,
SOC.FLNM3 || SOC.FLNM24 NAME, SOC.LSTNAM,
SOC.STREET, SOC.ADDR2, SOC.CITY, SOC.STATE, SOC.ZIP, SOC.ZIPPT2,
SOC.MEMBCD, DONOR, SOC.MEMSIN,
CAST(SOC.RFDLT AS CHAR(1)) RFDLT, SOC.NSTMEM, SOC.AFTMEM, SOC.LEVEL,
CVTNMDYTONUSA(BDAY, '1') DOB, TELENO, SEX,
SENDST,
CONDST, SOC.AD, LD, SOC.COUNTY, SDCODE, PRTYRG, REGSTD, RETCNL,
CAST(SOC.NMSUFX AS CHAR(10)) NMSUFX, MMDDYY2YYYYMMDD(SOC.DATE) DATE,
BLDGNO,
COALESCE(
(SELECT BLDNAME
FROM EMRBUILD
WHERE LOCAL = SOC.LOCNO AND BLDNUM = BLDGNO
ORDER BY LENGTH(TRIM(BLDNAME)) DESC
FETCH FIRST 1 ROWS ONLY), '') BUILDNAME,
CURPAY, ELEDST
FROM SOCMST SOC

UNION ALL
SELECT 'UFT' FILESOURCE, UFT.LOCNO, UFT.SOCSEC,
UFT.FLNM3 || UFT.FLNM24 NAME, UFT.LSTNAM,
UFT.STREET, UFT.NOST2, UFT.CITY, UFT.STATE, UFT.ZIP, UFT.ZIPPT2,
UFT.MEMBCD, DONOR, SUBSTR(DIGITS(MEMSIN), 5, 2),
CAST(' ' AS CHAR(1)), UFT.NSTMEM, UFT.AFTMEM, UFT.LEVEL, UFT.DOB DOB,
TELENO, SEX, UFT.SD,
CONDST, UFT.AD, LD, UFT.COUNTY, SDCODE, PRTYRG, REGSTD, '',
CAST(' ' AS CHAR(10)), CVTNUSATONISO(UFT.DATE ),
BLDGNO, '' BUILDNAME, CURPAY, ELEDST
FROM UFTMSTR UFT

UNION ALL
SELECT 'UUP' FILESOURCE, CAMP1 CONCAT CAMP2, UUP.SOCSEC,
UUP.FLNM3 || UUP.FLNM24 NAME, UUP.LSTNAM,
UUP.STREET, UUP.ADDR2, UUP.CITY, UUP.STATE, UUP.ZIP, UUP.ZIPPT2,
UUP.MEMBCD, DONOR, UUP.MEMSIN,
CAST(' ' AS CHAR(1)), UUP.NSTMEM, UUP.AFTMEM, UUP.LEVEL,
CVTNMDYTONUSA(UUP.BIRTHD, '1') DOB, TELENO, SEX,
DIGITS(SENATE),
UUP.CD, DIGITS(UUP.AD), SUBSTR(WARD, 1, 2), UUP.COUNTY, SDCODE, PRTYRG,
REGSTD, '',
CAST(' ' AS CHAR(10)), MMDDYY2YYYYMMDD(UUP.TRANDT ),
0, '' BUILDNAME, CURPAY, ED
FROM UUPMSTR UUP
WHERE MEMBCD <> 'C'

UNION ALL
SELECT 'PSC' FILESOURCE, PSC.LOCNO, PSC.SOCSEC,
PSC.FLNM3 || PSC.FLNM24 NAME, PSC.LSTNAM,
PSC.STREET, PMST.NOST2, PSC.CITY, PSC.STATE, PSC.ZIP, ZIPPT2,
PSC.MEMBCD, DONOR, PSC.MEMSIN,
CAST(' ' AS CHAR(1)), PSC.NSTMEM, PSC.AFTMEM, PSC.LEVEL,
CVTNMDYTONUSA(PMST.DOB, '1') DOB, PSC.TELENO, PSC.SEX,
CASE WHEN HEX(SN) <> '4040' THEN DIGITS(SN) ELSE ' ' END,
CONDST, DIGITS(ASMDST), SUBSTR(WARD, 1, 2), PSC.COUNTY, SDCODE, PRTYRG,
REGSTD, '',
CAST(' ' AS CHAR(10)), MMDDYY2YYYYMMDD(PSC.DATE ),
BLDGNO, '' BUILDNAME, CURPAY, BLK3
FROM PSCSOC PSC
LEFT JOIN PSCMST PMST ON PSC.SOCSEC = PMST.SOC

Wrapping it in a CTE takes 2 minutes.

with temp as (
-- the exact same 4 UNIONs
)
select *
from temp

Visual Explain is correct in that removing the UDFs does in fact speed
the thing up. The question is this: Why does wrapping this an a CTE
slow it down?