I have restarted UE and after that 252 of 256 LandscapeStreamingProxies is greyed out and I can’t see them. What should I do to see them like before restarting the UE?
You need to load those cells in world partition. Open the world partition mini map and select drag the cells you want to load, right click and a menu will popup that will allow you to load selected cells.
If you want to quickly load a specific proxy the you can right click it in the outliner and pin it.