I got this issue today as well. Probably today's update broke something. In my case, Stellaris stopped launching.
Resolved as following:
From C:\Users\YOUR_NAME\AppData\Local\Programs\Paradox Interactive moved today's folder to a safe location one level above...
View attachment 672658
So launcher is calling previous version now, which worked fine.
Doesn't work for me since I don't have the version .16 version in the folder. All I have is .11 and .17
So is the launcher still looking for version .16 even though version .17 was pushed out today?