Filters->Alphabetical can have too many entries for the size of the screen, preventing to select certain filters
When a user add custom filters (or have a small screen resolution) some filters are not clickable in Alphabetical submenu because it takes too much space on the screen:
A solution could be to add the following in pqProxyGroupMenuManager.cxx:populateMenu()
alphabeticalMenu->setStyleSheet("* { menu-scrollable: 1 }");
Wich give the following results :