After updating firmware to latest version, only the master was updated. This messed up connection to the slave AP - slave AP showed as disconnected.
After trying to factory reset multiple times (hold down reset button until power light is red) the R510 AP now shows solid green on power, and 2 sec blink pattern on CTL.
Now the web portal for Ruckus does not display the slave AP as disconnected, and no ConfigureMe network has been created from the slave AP.
Additional info: these two Ruckus units are plugged into the same PoE switch. PoE switch is brand new, and the setup worked before attempting to update the Ruckus firmware, so it is unlikely to be the point of failure.
At this point I am thinking I will need to buy a PoE injector and connect the slave AP to my PC to reach the web client for the slave to properly factory reset and update the firmware.