It was working in 3.7, upgraded to 3.10.3, it is a new VM and did a back up and restore to upgrade. Using same Splunk cisco PI add-on version 2.1.2. There is no output when querying in Splunk. Hostname was changed in PI with this upgrade but IP address is the same, the new PI hostname was changed in Splunk.
If so, I'm guessing you should put the credentials again. I recommended to reset the nbi read only account in the PI, and re-enter it into the splunk add on account too. Also, please try reboot the Splunk. Sorry for not helping much, but we had similar issues after upgrade from 3.9.x to 3.10.3. also, try to remove inputs and recreate them. Sometimes, splunk holds old connections.