Comment 5 for bug 1847896

I haven't tested this, but since seb128 pasted the relevant messages in IRC.

I bet you that it's because polkit isn't considering the D-Bus session of the greeter to be 'active', because it's not finding it.

If someone would like to test build a systemd with this commit included:

https://github.com/systemd/systemd/commit/a2dcb1d78737d3daa301ee63fbdd02837acb71a8

I suspect the problem would be fixed.