Hey Footman,
Currently El Capitan (10.11) is unsupported.We’re using OS X 10.11 El Capitan internally and we’re working closely with Apple on support for it (including the new renderer). However, the currently released beta version of 10.11 is evolving too rapidly and there are too many things left to do on both Apple and Epic sides that we cannot simply add official support to 4.9 (or 4.8) at this point.
As the new OS X matures and is closer to release (which we expect to be in late October) we will most likely start officially supporting 10.11 in UE 4.10 and release patches/QFEs for older UE4 versions.
Thank you for taking the time to report this issue, and if you have any further questions please let me know.
Regards,