Glitchinf occurs on timeline and export

[GAVINSF]

does anyone know why this happens?

Does anyone know why this happens? and also the video then exports like this, glitching throughout 

[John V Knowles]

This is typically a GPU issue. What GFX card do you have and how much VRAM does it have? Are your drivers up to date? 

If you go into the Project Settings and change the renderer to Software Only, does the issue go away?

[Peru Bob]

Are you using a Mac?