Sorry, forget to mention that I removed all of the CC_LIBRARIES_PANEL_EXTENSION folders
1. I actually made a zipfile on my dekstop (just in case as a backup) and dragged all the CC_LIBRARIES_PANEL_EXTENSION_xxxx folders into the zip-file.
2. After completion, I deleted all of the CC_LIBRARIES_PANEL_EXTENSION_xxxx folders.
3. Then used the AdobeCreativeCloudCleanerTool: All - CC Library (32 Bit)(3.1.3).
4. After that I installed the CCLibrary extension from https://helpx.adobe.com/creative-cloud/kb/libraries-panel-not-working.html (After installation, I had 6 folders instead of the original 11 that were in C:\Program Files (x86)\Common Files\Adobe\CEP\extensions\ - most likely old versions that conflicted with the new CC Library version)
5. After that everything worked great again.
I'm using Windows 10 Pro and the original problem was not found on Photoshop but on Indesign 2020 Prelease (and also 2019) and Bridge 9.1. Illustrator and Photoshop 32bit (2018) and 64bit (2019) also showed the same erratic behaviour.