After adding a fourth 'library location' it does not appear in the available list of asset libraries

The 'Library locations' screen already had three entries and I was able to add a fourth. However, it did not appear in the list of available libraries under 'Assets'. I tried adding the fourth library both in the UI and in the Windows registry, where I also incremented the size key in the pathInfos registry entry as suggested in the documentation.

https://substance3d.adobe.com/documentation/spdoc/editing-resource-paths-manually-172824761.html

I had to remove one of the library locations so I had a total of three rather than four, for my added library to be recognized.

I don't see any reference to there being a limit to the number of library locations and would like to know how I can add a fourth library.

Thanks in advance for your help.