Dear experts,
   I have a logbook which has authentication as follow

Authentication = LDAP, File
Password file = PASSWD.file
LDAP server = ldaps://it-ldap-XXX.XXX.XX:1636
LDAP userbase = ou=people,ou=RGY,o=XXX,c=XX
LDAP login attribute = uid
LDAP register = 0
Self register = 0
Allow password change = 0

Some of the my user (but not all) have issue in accessing this protected elogbook.
The ldap password is correct (we checked).
What I see in the log is as follow:

22-Feb-2021 11:25:51 [XXX.YYY.ZZZ.QQ] {Beam Run} LOGIN user "USERNAME" (attempt)
22-Feb-2021 11:25:59 [XXX.YYY.ZZZ.QQ] {Beam Run} LOGIN user "USERNAME" (attempt)

The user USERNAME is present in PASSWD.file.

For other user, for which the login works, I do see an (attempt) and then (success)

we tried the standard stuff: clear cache/cookies and with different browser. We also tried to remove the user from PASSWD.file and 
create it again, but nothing has worked.

Any suggestion how I can debug this problem?

Thanks in advance,
  Stefano