Frame drop Diagnoses

Hey there!
I am creating a small level with an indoor and outdoor environment which had a file error somewhere down the line that I could not quite pinpoint. The backup was also messed up so it’s possible I did something wrong, but now when I have my lighting baked my framerate for the very same scene went from 100fps to 50-55fps without any changes. This is on Unreal 4.10.

What is/are the best methods for diagnosing such problems?

Other things that co-incide with around this time is I downloaded the later engines and booted up the file on 4.11, but not saved/reverted to my backup so is still 4.10 file on 4.10 engine.