When locking read-only levels (via Levels->context menu), each frame we check that both the package exists on disk and whether the file is read-only. Performing this each tick can cause a substantial decrease in editor performance.
UDN Post has additional info.
i have this problem UE4CC-Windows-58DC12AF4B97F057BD108FBFF569B2E9_0000
Status update on UE-21075 and UE-20622?
Delay nodes occasionally don't fire the "Completed" output in a nativized build
Undefined sysmbol: typeinfo for AActor when cross-compile linux dedicated server on windows
I am not able to find world outliner how to enable it?
Installer 4.10 failed with error code R-1603
An error occurred while trying to generate project files !?
How to achieve HLSL Multiple Render Target in Material blueprints?
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-20672 in the post.