Just a suggestion.
It already takes a while to test anything in UEFN going back and forth sometimes. (+ some strange system mouse lag that keep popping up)
Fortnite servers keep dropping lately as well, that also means you can’t even get into the UEFN editor and test anything.
Also noticed it might be my buggy infinite loops in verse that might be dropping the servers 
as they dropped precisely when I was testing new stuff last few times… most likely not , but who knows