This is the output of id www-data. Just for your information! I added web33 yesterday manually. My new test user I created today (web34) is missing. It wasn't added automatically nor manually
# id www-data
uid=33(www-data) gid=33(www-data) Gruppen=10000(web1),10002(web21),10003(web20),10004(web18),10005(web19),10007(web15),10008(web8),10009(web6),10010(web5),10011(web2),10012(web9),10013(web11),10014(web10),10017(web3),10018(web24),10022(web28),10023(wordpress),10025(web30),10027(web31),10029(web32),10030(web33),10031(web34),33(www-data)
Attached you find the Webserver settings of froxlor. The username / group is www-data