Subquery in INSERT works in SQL but not PDO
I could fix your problem, with the insert
INSERT INTO tab (id, seUuid4, rxUuid4, text)
SELECT
    1,
   IFNULL ((SELECT  uuid4 FROM otherTab WHERE lgUuid4 = UNHEX('00001234aaaa4444aaaa432187654321') AND data = 'JPK' LIMIT 0,1) IS NULL,0),
    (SELECT uuid4 FROM otherTab WHERE lgUuid4 = UNHEX('12340000bbbb6666bbbb432187654321') AND data = 'TXT' LIMIT 0,1),
    'some text';

but this gives following error

Schema Error: Error: ER_NO_REFERENCED_ROW_2: Cannot add or update a child row: a foreign key constraint fails (test.tab, CONSTRAINT tab_ibfk_2 FOREIGN KEY (seUuid4) REFERENCES otherTab (uuid4))

Which means that you must enter there a uuid, which is exists