I have three machines running Xubuntu: two on 16.04 and one on 18.04.
psensor is installed on all machines, and the
sensor preferences for CPU core temp (or whatever) on all machines has the setting
Display sensor info in the label (experimental) enabled.
The sensor info is properly displayed in the label for both 16.04 machines, but not for 18.04. All required dependencies have been installed for
Xubuntu 16.04 has been installed on the currently 18.04 machine previously, and
psensor properly worked.
According to the Xubuntu 18.04 release notes, there have been some changes or updates to panel plugins, including the "Status Notifier Plugin" and a new "Notification Plugin". Since
psensor displays in the "Notification area" plugin (
systray-4), I'm guessing that some of these changes has affected the way
psensor and likely other applications are displayed?
I've included a screencap of psensor in label, that shows how
psensor label displays in the panel, as well as the
psensor settings. As you can see, it shows the temperature icon in the panel, but no actual sensor information. Furthermore, when you click on the temp icon, it no longer displays the summary/preview of temperatures and info, but instead opens the "Psensor - Temperature Monitor" graph.
This is the only issue I've had with Xubuntu 18.04 so far that bothers me (some other weird issues like file text persisting after you eject a drive), and really the only reason I have not updated my other machines to 18.04 already.
I haven't seen anyone else talk about this issue with psensor on 18.04, so either this is an isolated problem, or more likely, just a Xubuntu/XFCE issue rather than a Ubuntu 18.04 issue.