Comment 2 for bug 2038121

Thank you for taking the time to report this bug and helping to make Ubuntu better.

Bug reporting is about finding & fixing problems thus preventing future users from hitting the same bug.

I suspect a Support site would be more appropriate, eg. https://answers.launchpad.net/ubuntu. You can also find help with your problem in the support forum of your local Ubuntu community http://loco.ubuntu.com/ or asking at https://askubuntu.com or https://ubuntuforums.org, or for more support options please look at https://discourse.ubuntu.com/t/community-support/709

( Your details are unclean; pcmanfm you mention in the description is a different app to pcmanfm-qt. pcmanfm created by PCMan (https://github.com/PCMan) was both file manager and handles desktop of LXDE, with a Qt5 port of it called pcmanfm-qt used by LXQt; you filed against a different app to your description. Powering down may have triggered your issue because the file-systems were left in an unclean state (maybe safely causing shutdown via SysRq command would have been better) either way details currently are unclear & I suspect support maybe a better option; as user behavior may have contributed to this issue )