User listed in group but not in getent passwd

On a specific machine with both local users and LDAP users, there is a user that is listed under getent group foo (let's say the user jdoe is listed), but when doing getent passwd jdoe I get no output. Attempting sudo su jdoe doesn't work either. Using the command members -t foo I found out the user is only listed as a secondary member of the group, although I'm not sure if that's relevant. Does anyone know how I can find out how this seemingly nonexistent user ended up in this user group? To clarify, the listed user is in no way related to a system user, and it doesn't seem to be listed anywhere under locally created users. Something that might be a possibility: is it possible this is being caused by someone who previously had a user account named jdoe, whose account since has been renamed or deleted? And if so, how can I find this out? This is my /etc/nsswitch.conf:

-none
passwd:         compat ldap systemd
group:          compat ldap systemd
shadow:         compat ldap

hosts:          files dns
networks:       files

protocols:      db files
services:       db files
ethers:         db files
rpc:            db files

netgroup:       nis

It is pretty much the default configuration with LDAP included.