Repo discovery only works one at a time
Not sure about the real symptoms but here is what happened:
Repo discovery in org A for url http://ftp.linux.ncsu.edu/pub/epel/6/x86_64/
Create a new product
Switch to org B
Repo discovery in org B for url http://ftp.linux.ncsu.edu/pub/epel/6/x86_64/
UI page remains blank. Discovery task is listed and looks like it succeeds in B. No JS errors.
Once sync is complete in org A, retry discovery in org B and it works