Hello wukakuki,
I have a couple of questions that should help narrow down where the issue is.
1.) Is this build from a copied project from an older version of the engine to 4.9?
2.) Can you reproduce this in a new blank project?
3.) Does it actually stop or does it take a really long time to get to 1%?
4.) Can you link me your DxDiag?
After I have this information I will continue to investigate this issue and hopefully pinpoint the problem.
Thank you,