Screen black after closing

Hey,

When I close my computer screen lid and open it again the majority of the screen stays black except for a bar along the top which is showing my wallpaper. It sometimes stays like this for a few minutes or a few seconds.

When the screen was black I took a screen shot - but the image of the screenshot actually shows the screen working as normal. So I had to take a picture with my phone to show the issues.

I've attached a pictures to show what I mean. Anyone know what is going on here?

Mac is fully up to date and is a (13-inch, 2019, Four Thunderbolt 3 ports)