I'm running kruler on a Fedora 25 Box with creen-size: 1920x1080. If I'm running kruler, it is almost unusable because the ruler's text is overlapping. Therefore I filed a RedHat BZ ( see https://bugzilla.redhat.com/show_bug.cgi?id=1428784) and got the suggestion from the advisor to file a KDE BZ. You will find details there (including a screen shot).
I can confirm that configured "Small" font/size can result in the symptoms described here. For me, default "Sans Serif 8" was fine, but making it any bigger started getting overlap.
*** Bug 383229 has been marked as a duplicate of this bug. ***
Resolved with Aurélien's patches.
*** Bug 345069 has been marked as a duplicate of this bug. ***