How to solve crash in game startup for iOS and Android device

I have builded iPa and Apk file, but they all crashed in game startup, how I can fix or how to bedbug crash,
Could I get any log file, if yes where are log is, I have builded 3days all day, could any one can help me,
Thanks, My Editor is 4.5.1

Hi Alex,

Thank you for your report. We were not able to investigate this on the engine version you reported, but there have been many version changes to UE4 since this question was first posted. With a new version of the Engine comes new fixes and it is possible that this issue has changed or may no longer occur. Due to timetable of when this issue was first posted, we are marking this post as resolved for tracking purposes. If you are still experiencing the issue you reported in the current engine version, then please respond to this message with additional information and we will investigate as soon as possible. If you are experiencing a similar, but different issue at this time, could you please submit a new report for it.