By any chance had these users entered the grace period
before you changed their profile?
Once an account is in the grace period, to get out of it you have to reset the password. Just changing the profile isn't enough.
Your new profile has a 7 day grace period. So a week later these passwords expire!
create profile short_pwd limit
PASSWORD_LIFE_TIME 1/1440 PASSWORD_GRACE_TIME 1/1440;
create profile unlimited_pwd limit
PASSWORD_LIFE_TIME unlimited PASSWORD_GRACE_TIME 1/1440;
create user usr identified by usr profile short_pwd;
grant create session to usr;
select account_status, expiry_date, sysdate from dba_users
where username = 'USR';
ACCOUNT_STATUS EXPIRY_DATE SYSDATE
OPEN 10-APR-2017 02:44:09 10-APR-2017 02:43:10
exec dbms_lock.sleep(61);
conn usr/usr
conn chris/chris
alter user usr profile unlimited_pwd;
select account_status, to_char(expiry_date, 'HH24:MI:SS') exp, to_char(sysdate, 'HH24:MI:SS') dt
from dba_users
where username = 'USR';
ACCOUNT_STATUS EXP DT
EXPIRED(GRACE) 02:45:13 02:44:22
exec dbms_lock.sleep(61);
conn usr/usr
ORA-28001: the password has expired
conn chris/chris
select account_status, to_char(expiry_date, 'HH24:MI:SS') exp, to_char(sysdate, 'HH24:MI:SS') dt
from dba_users
where username = 'USR';
ACCOUNT_STATUS EXP DT
EXPIRED 02:45:13 02:45:57