As I know LS uses lastlog for detect last login of users.
So if you have non-english console then parser not works. If you login by domain user then lastlog doesn't work also.
I suggest change script to use another utility:
loginctl list-sessions
and loginctl show-session for Timestamp info
Also there is another issue:
LS doesn't show last user on the linux assets and we cannot search by linux logon username.
Please improve Linux support!