we are migrating our SP2016 sites to a new SP2019 OnPremise farm.
We use our own Masterpage, css, spcolor and spfonts files for custom theming. All works fine in SP2016. But when we test our sitecollections in SP2019, not all users sees our company theme. Some users (visitors with small range of permissions) see some parts of our theme(Masterpage and css) but not the colors set by spcolor file. The tiles on the site content page are still in blue color, not in our company green. One cause could be our own permission level for visitors, in that we have removed the "Browse Directories - Enumerate files and folders in a Web site using SharePoint Designer and Web DAV interfaces." level for some reasons. If I add this permission to our visitor permissionlevel, they will see our complete company theme. Libraries for Masterpages and Themes are readable for all users.