I had a similar problem after upgrading FMS from v15 to v16. Not sure if my solution will work for you.
My issue was caused by a conflict with two plugins used by Adobe Acrobat Reader DC.
I moved the AdobePDFViewer.plugin and the AdobePDFNPAPI.plugin from the Internet Plug-Ins folder in the Library folder to the Disabled Plug-Ins folder.
When moving the plug-ins, macOS copies them so I had to then delete the copies remaining in the Internet Plug-Ins folder.
Restarted my computer and all my PDF files stored in containers were visible again.