I had this happen to me today. I did 2 things that remedied the issue, not sure what did the trick?
First I logged in to my account on my steinberg. I immediately noticed that nothing remained in my account. No downloads or elicense. I had the email with the original download code and activation code. I reentered both and now all appeared.
Second, I had installed the SKI remote so I could use use my iPad to begin recording. Unfortunately I could not get it to work??? So I uninstalled it from windows.
After a reboot Cubase 9 came up as it did the day before. I assume the server going down yesterday was the primary reason for the problem, but can’t say for certain.
Hope this helps!