We have identified a new issue with the Launcher where the yellow [Launch Unreal Engine 4.7.3] button is automatically downloading and installing the latest hotfix. This is not intentional behavior, since only clicking the [Update] button should cause the update to occur. If you are on 4.7.3 and and do not wish to update at this time, you can continue using 4.7.3 by launching directly into your project from the Library, or by using the Launcher in “Offline Mode”.
Additionally, we are currently investigating some reports of Blueprint crashes after updating to 4.7.4. If you also experience a crash in your project upon startup after updating to 4.7.4, please let us know by making a report to the Bug Reports section of the AnswerHub (follow link in my signature).
Thank you, and we apologize for the inconveniences from either of these issues.