In Dec 2021, i have verified that if you set up a chroot with an LDAP client set to connect to a non-existant ldap server chklastlog and chkrootkit still works, so the issue isnt that something is always reaching out to the LDAP server and hanging when there is no response.
But it may be that you need to log in and log out using LDAP credentials to get something problematic in wtmp/lastlog. So the next step is to set up a "real" ldap server in case some ldap-related things end up in wtmp.
