Need help - 3D viewport blackscreen


I hope I’m in the right place.
As you can read, I need some help concerning the 3Dviewport (I’m a very newbie)

Short story, I’ve created a new level, added some mesh and assembling them together, then saving the project with Ctrl+s, naming it “InTheSea”, then I close Unreal Engine 4.22.
Seconds later, I open the project, click on “file” then “open level” and I select “InTheSea”.
Instead of showing what I last saved, the 3Dviweport is showing me a blackscreen.

What happened ? How can I fix it ? Help.

I will gladly provide more information if it can help.