the problem is : there is an error in your code , open vs file and try to solve error and rebuild project
if it rebuild without error then your project will start normally
In Version 4.20, I tried recompiling in DebugGame_Editor mode for many times, but it did not work.
To my surprise, when I switch to DevelopmentGame_Editor model and compile it in VS, I find that the hotload DLLs are cleaned and rebuilt, and I open the uproject file successfully in the editor.
On linux : Removed all files in /MyProjectFolder/Binaries/Linux
On next run it asked if i would like to rebuild the modules, clicked yes, project is now useable.