Just so we are clear:
Google Voice is not a standalone telephone company (this is an important legal and regulatory distinction). It's a call forwarding service. You get (or port in) an inbound Google Voice number, and then you configure that number to forward to up to six, ten-digit PSTN phone numbers. Optionally, Google Voice can forward to Google Chat (Google's own Chat service is defunct, but it is leaving in place the underlying XMPP protocol used by Chat for OBi users). OBi devices act as XMPP/Chat clients. So, an OBi device is answering forwarded calls, similar to answering the call on a land line or mobile phone number.
If a Google Voice number can successfully forward calls to a PSTN number, and Google Chat is check-marked on that Google Voice configuration, then the OBi should ring on inbound calls to that number. That is why I asked you to test it. You cannot have a mobile phone added as a forwarding number on two different Google Voice configurations. This is a technical limitation of the service, related to the method Google Voice uses to handle text messaging. If you define the forwarding phone as a land line number on both of two GV configurations, then it can exist on a maximum of two GV accounts, but text message forwarding between that number and GV will be disabled.
Now, all that is great, but it doesn't explain why you are having this problem.
The fact that the suspect GV account actually works when it is configured on SP1 further exonerates Google Voice as the cause of the problem, if I am reading your posts correctly.
I have no idea how SP2 could not be ringing, unless you have made some change to the SP2 settings that is disabling it, or SP2's two-ring cadence doesn't work on your phone. When a call is forwarded to the OBi on SP2, watch the LEDs on the OBi and see if the phone LED blinks. If it does, pick up the phone and see if you can answer the call. If that's the case, then you have a ringer issue. Try using a different telephone plugged into the OBi; preferably a different brand. We can fix the ring cadence if that turns out to be the problem.
You can certainly try moving the account off of SP2 onto SP3 or SP4 as Robert suggested.