After restarting Unreal 4.26 nothing in my project is visible in the perspective or camera viewport

After restarting Unreal nothing in my project is visible in the perspective or camera viewport
What can cause this issue?

Here is a screen capture:

I posted in the Unreal Forums here:
https://forums.unrealengine.com/development-discussion/content-creation/1854521-nothing-on-my-level-is-visible-on-perspective-or-camera-view-after-ue-restart

Is this thing only happening to me?