We have Exchange 2019, including email public folders, upgraded from previous versions.
Today I was in ECP as domain admin, and tried to change permissions of one of the groups with permissions to some folder (which has subfolders) from Custom to just "Folder visible". Hit Save, with "Apply changes to this public folder and all its subfolders" checked. The progress bar shows 1 block right away and never advances. After a few minutes: "Array dimensions exceeded supported range." There are literally zero web pages with this error in combination with Exchange (tried Bing and Google), so I'm not holding out much hope, but if you know what my next step should be, I am all ears.
