I've got a PCLOS KDE virtual machine set up, so something must've been reported about Sigil and that particular Linux distro in the past, but unfortunately, I can't duplicate the issue. My PCLOS VM has Qt5.9.1 rather than 5.9.2, but I have no issues with Sigil/5.9.2 on any other distros.
I've found this:
http://www.pclinuxos.com/forum/index.php?topic=144184.0
But they seem to be referring to the sigil 0.9.8-3 synaptic package and the version I have installed (and the only version showing as available) is 0.9.8-2.
If they've broken something with their latest sigil package (or their Qt packages), the only thing I can recommend is uninstalling the synaptics version and using my stand-alone Sigil installer from the
stickied threads above.
EDIT: I've updated to sigil 0.9.8-3 on PCLOS KDE and still can't reproduce the error (still sticking with Qt5.9.2 for now). Best guess is that pclos broke something in their most recent qtwebkit and/or libxml2 packages.