If app doesn't respond that doesn't respond that doesn't mean that it slowed down, It may be crashed.
it respond, only show this message.
Why don't you stop your program in debugger and see where it hangs?
Or you can use profiler. Or logging.
Its a good thing use a debug, but I could not figure out while using a debugger, because the only this message appears and nothing changes, so like eXpl0it3r said is a thing of treating window events
Are you processing the SFML events? You have to otherwise the OS marks your application as unresponsive.
So if I do something that takes a long time and forget to treating events this message will appear?
Like loading many things to the game and/or making random procedural generation content.
I solved creating the window just after loading everything, and functions / methods that require a valid OpenGL context, I put a sf :: Context, then that means solved, thanks
now i will try to make a loading screen and see how deal without using threads, or just ignoring the window events.