I use Grandstream ATA 486 to connect phone to Asterisk box. For incoming calls, it rings sometimes, but sometimes not. Anyone has any idea why?
it doesn’t like you. Sometimes you get on its good side though and it works.
It’s also possible that a technical problem is causing a malfunction, but to determine that we will need more info- are they on the same network, how are they setup, relevant sip.conf/extensions.conf segments, and most importantly what do you see on the Asterisk CLI when it doesn’t work?
or the chicken that was sacrificed was the wrong breed 
hehehehe yes that can cause huge major problems… 