It seems as if the Catalog Explorer can only display a maximum of 1000 folders within a UC Volume. I just ran into this issue when I added new folders to a volume which were not displayed in the Catalog Explorer (only folders 1-1000). I was able to read them in a notebook and the also show up in the ADLS, just not in the Catalog Explorer. Also, I was not able to search for the folder in the search box of the catalog explorer.

Is that a known limitation?