All directory navigation more than a couple of levels crashes.

A few weeks ago Thunar started crashing when I tried to navigate any more than 2 or 3 levels from the folder shown at startup. Now I can't even start Thunar from the GUI, and when I start it from a terminal all I get is "Segmentation fault (core dumped)". Nautilus does the same. Dolphin and Krusader don't. Earlier when I started gedit and tried to open a file that required navigating any more than 2 or 3 levels from where the dialog started, there would be delay when I selected the last folder to open and then gedit would crash. Now when I start gedit from the gui, nothing happens; and from a terminal I get the same "Segmentation fault (core dumped)" error. It doesn't matter what program I use, if I try to open something that requires navigating more than 2 or 3 levels from where the open dialog started, there's a delay when I select the last folder to open and then that program crashes with the same error. However, if I navigate to a folder in Krusader and double-click on a .JPG file, Kolourpaint opens with the file loaded; then, if I try to save the file in a different folder, I can. However, double-clicking or using "open with" on a .TXT file does not successfully start gedit, though it will start mousepad...but if I then try to save the text file in a path that requires navigating down a couple of levels, mousepad crashes. Note that all these crashes are registered as such and generate the GUI error "The application [name] has closed unexpectedly. Send a problem report to the developers?", which I do; though I'm never asked anything about what I was doing when the crash occurred.

I did find that programs installed with snap didn't have the same problems, but the snap installation isolates them in a way that doesn't allow me to navigate anywhere outside the snap folder. I have done recovery starts of Ubuntu, checked the file system, checked system memory, and found nothing wrong. Firefox and Chromium work find, until I try to save a download in a folder more than 2 or 3 levels deeper from the one the save/save as dialog starts in, or try to load a file more than 2 or 3 levels deeper from the one the open dialog starts in. Navigating up doesn't seem to be a problem, and navigating within shared folders on the machine from the network works fine.

If I start Win XP Pro in a VirtualBox VM, navigation into shared folders using the Windows file explorer isn't a problem. If I start Sigil and select open, the selection window appears, nothing happens, and then Sigil crashes. Starting from a terminal tells me that Sigil is generating the same segmentation fault as above. However, if I start Sigil and open a file from the File menu's list of previously opened files, no problem and no problem saving changes...as long as I don't try to save the changes somewhere that requires navigating 2 or 3 levels down.

I don't know if this is a linux system bug or a XFCE-4 bug, but it makes the machine pretty frustrating.

ProblemType: Bug
DistroRelease: Ubuntu 18.04
Package: thunar 1.6.15-0ubuntu1.18.04.1
ProcVersionSignature: Ubuntu 4.15.0-118.119-generic 4.15.18
Uname: Linux 4.15.0-118-generic x86_64
ApportVersion: 2.20.9-0ubuntu7.17
Architecture: amd64
CurrentDesktop: XFCE
Date: Wed Sep 23 23:49:59 2020
InstallationDate: Installed on 2019-11-29 (299 days ago)
InstallationMedia: Xubuntu 18.04 LTS "Bionic Beaver" - Release amd64 (20180426)
ProcEnviron:
 LANGUAGE=en_US
 PATH=(custom, no user)
 XDG_RUNTIME_DIR=<set>
 LANG=en_US.UTF-8
 SHELL=/bin/bash
SourcePackage: thunar
UpgradeStatus: No upgrade log present (probably fresh install)