Lightroom Classic Catalog Malfunction

Usually that's an indicator of catalog corruption. 

Based on the fact that only one preview is visible, I'm going to suggest renaming the X Previews.lrdata file, where X is your catalog name. You may have a corrupt previews database. If this works, delete the renamed file and allow Lightroom to rebuild previews. Yes it's tedious. If it doesn't work, rename the file back again as it wasn't the issue and my guess is wrong. 

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A first step is try to to reset the preferences to the default settings.

• Reset Procedure:
• Close Lightroom.
• Windows: Hold down [Alt]+[Shift] while restarting Lightroom.
• Mac: Hold down [Opt]+[Shift] while restarting Lightroom.
• Overwrite the Preferences when prompted by the dialog.
• Close Lightroom.
• Restart Lightroom.

It's recommended to backup your preferences before you reset the preferences to the default settings: 

https://helpx.adobe.com/lightroom-classic/kb/preference-file-and-other-file-locations.html

Please check if you have full access to the folder where the Lightroom catalog is located.

Is your system up-to-date? All updates, patches, device and chipset driver installed?

Please provide also a copy of your 'System Info'. This can be get from the LrC Help > System Info menu item.

There's a copy button in the System Info dialog. Press this button and paste the info into your next forum post.