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UE 4.19 just exploded. How to repair it?

I was using UE 4.19, I showed the Engine hidden content in the ContentBrowser and attempted to do a slight modification to the default material used to display particles in Cascade, when I hit save the engine attempted to save it but it frozen instead.
After waiting servel minutes, I attempted to CTRL+ALT+CANC and force the engine to shut down, this instead frooze everything else and a message saying that Windows stopped responding appeared. I just restarted my machine manually.

After restart, I opened the launcher and the image below is what I see.
Not only 4.19 is missing, but is missing even the option to install it. How do I make it come back?!

EDIT: I closed and launched the launcher again, now 4.19 is there again!!! I don’t know what’s going on O_O