Sua consulta SELECT não tem uma cláusula GROUP BY. Provavelmente você quer dizer:
INSERT INTO appfilter2
SELECT userapps.name, GROUP_CONCAT(CONCAT(userapps.activity, '/',userapps.class)) AS activity
FROM userapps
GROUP BY userapps.name
INSERT INTO appfilter2
SELECT userapps.name, GROUP_CONCAT(CONCAT(userapps.activity, '/',userapps.class)) AS activity
FROM userapps
GROUP BY userapps.name