I am using Linux Mint 19. When displaying slides the screen flickers 3 times. I tried LibreOffice for Windows. No problems. Slides displayed with no screen flickers. Why is this happening with Linux?
LibreOffice Impress is a little buggy. I will continue to use Office365 PowerPoint.
Problem Solved! The reason the screen flickers when displaying slides has to do with slide transitions. I removed all slide the transitions. I tested this under Linux and Windows. Problem solved!
Now I can transition over to Linux from Windows.