Basic actors invisible when placed into the scene

I can not find an answer anywhere. When I drag any actor from the side bar ( cube or light e.g.) I can only see gizmo and no object at all. New actor’s name is in Details, but not in the Outliner. I’m new to UE4 and I’m completely stuck, please, help!

UPD: It somehow magically fixed itself for some time, and then came back. All above is also true for any object from content folder. Reopening project doesn’t seem to help.

There on ttop of general view are menus. And one of them has list of classes that are visible in viewport.

Everything I need is checked visible there. For now I reopened editor and everything seems to work again, but the other time I tried the same it didn’t have any effect

There are also keyboard shortcuts to show/hide stuff and maybe menu did not update.
search for (some decent result) of “UE4 Editor HotKey Cheat Sheet”
there are keys to show/hide classes, and some keys for render mode.
You could switch to render only lights or only landscape etc.
Or you could hide actors.

Thank you, I will try it.