Windows 10: Desktop Icons Disappeared and Taskbar Icons Changed

I have a laptop with a 4k 17.3" display. When set to native resolution, 3840x2160, some programs do not display their dialog boxes and menus in usable form. In an attempt to correct this I have tried setting the display resolution to 1920x1080. Then setting the magnification to 100%. At 4k resolution it is set to 250%. When I change the resolution down the dialogs and menus become usable, however all the desktop icons disappear and the icons pinned to the taskbar all change to the same graphic, I can't tell what it is. If I change the resolution back to 4k the icons become normal again. Any ideas?

:)

 

Icons

In Windows 10: Icons have disappeared from desktop and from listings of documents, downloads and pictures. Non Microsoft icon in taskbar have changed to generic icon. Resetting to a date prior to disappearance did not work.

 

My taskbar icons disappear

I am using Windows 10. In my desktop I have icons in the taskbar. These open OK but when I close any icon the rest of the icons all disappear in the taskbar even though the task bar is 'locked'. There is a white vertical bar in the taskbar to the right
of the icons with up and down arrows. When the icons have disappeared if I click on the up arrow they all appear again. This is a pain having to do this everytime. What is the point of 'Lock the taskbar'. How do I stop these icons from disappearing?