The last version of evince on Lubuntu 18.04 has stop the thumbnails preview in pcmanfm.
I solved the problem doing a downgrade:
sudo apt-cache show evince sudo apt install -y libevdocument3-4=3.28.2-1 sudo apt install -y libevview3-3=3.28.2-1 sudo apt install -y evince=3.28.2-1
Anyone knows how update without crash this feature?
I am waiting for 20.04, but I will continue using LXDE because LXQt don’t work with themes like LXDE.