See AnswerHub thread for why this was marked "By Design"
When you have a character in a level and if you setup the blueprint of the character as shown below, the rotation of the character will differ when played Standalone vs Selected Viewport.
Photo of Blueprint setup is attached below
Link to Project
1) Download the attached zip file
2) Unzip the content of the zip file into your Unreal Projects
3) Once placed into your projects folder, double click the uproject file to open the project.
4) When in the Project, Select play in viewport.
5) Use an Xbox controller and use the right thumbstick to rotate the character.
6) Stop playing in Selected Viewport and then play in Standalone.
7) Use the Xbox controller and rotate the character
8) You will be able to see a speed difference between the two play options
Head over to the existing Questions & Answers thread and let us know what's up.