I have 2 issues.
first: I was on my browser the ERR_NETWORK_ACCESS_DENIED error when i try to get to the R local help server (http://127.0.0.1:x
You only need to turn off Windows Firewall.
I did it and succeeded.
I had this problem and in the end reinstalled studio, turned on/off the firewall, reset netsh, etc. etc. all failed.
Gradle needed to be upgraded and once upgraded it worked fine.
There was not message to tell me this.
This is what worked for me I hope it helps as there is not much information on this error.