I was launching Fortnite. After clicking Launch button in client it begins loading Fortnite and around after 30 secs it stops. All other sections are working (i.e. chat, friend list, etc.). I tried to launch Fortnite several times since yesterday, it is not working. Always the same Unreal Engine 4 Crash Reporter pops up.
This started to happen yesterday 16.11.2018 at around 16.00 CET. I am unable to send this via crash reporter (send option is grayed out) so I hope this will help you to investigate.