Yup, Rstudio doesn't work for me either upon install.
RStudio Edition: RStudio Desktop
RStudio Version: 1.1.453
OS Version: MacOS High Sierra 10.13.4
R Version: R 3.4.4 GUI 1.70 El Capitan build
I also posted about it here and got no responses that could help me: R Studio Desktop Won't Start on macOSX High Sierra
Similar to you, RStudio works in safe mode, and I am able to ping localhost and 127.0.0.1 in normal boot mode.