Yes, I’m fully aware of it being a biasing issue, but there are ways you can get around it by playing with the number of cascades(at three, it’s almost non-existent), exponent and max distance. Even though UE isn’t using slope biasing, it is still using some kind of biasing/filtering.
After doing some research on CSMs, I see PCF and VSM coming up a lot, but nothing about them using slope biasing; with CSMs. I think slope biasing is only used for regular shadow mapping. It might boil down to a CPU vs GPU computing issue or it might be a forward vs deferred issue.
Regular shadow mapping mentions slope scale depth biasing:
https://msdn.microsoft.com/en-us/library/windows/desktop/ee416324(v=vs.85).aspx
On that same page(the first link), there is a link to another article about CSMing says nothing about SSDB and only mentions PCF/VSM: https://msdn.microsoft.com/en-us/library/windows/desktop/ee416307(v=vs.85).aspx
Also, this brings up some of the issues with trying to use slope biasing in screen space: https://mynameismjp.wordpress.com/2013/09/10/shadow-maps/
I’ll keep doing more research on it all, but I’m pretty sure that the Unreal devs know all the tricks and standards for something like shadow mapping.