I had the same issue on my own project too.
The issue was with the Blueprint Character class (I don’t know what exactly was wrong).
I knew the things I was changing and, so, I was removing all lastly changed items one by one and with each removed item I was trying to launch my project from the Visual Studio. I removed (more precisely - I moved these items to other, not project related, directory) from my project (including some bp widgets, bp game instance class, and the character bp class) and, finally, the project started successfully. And while the editor was launched I returned all the “removed” items.
I hope it will help. Good luck.