Comment 2 for bug 1781418

I found the solution here: https://unix.stackexchange.com/questions/454593/groups-not-registering-in-x
It seems to be caused by an update to libpam-kwallet5.
Uncommenting the following lines in /etc/pam.d/lightdm resolved the issue:

```
auth optional pam_kwallet.so
auth optional pam_kwallet5.so
```

I'm not sure whether the package maintainer of libpam-kwallet or the package maintainer of lightdm might have to add this change to their packages - or if it maybe only affects old installations.