Option Bus NAC Outputs (FPP-RNAC-8A-4C) will never be in sync with the NAC Output of the panel (FPA-1000, FPA-1000-UL, FPA-1000-V2, or FPD-7024).
1.) Add another FPP-RNAC-8A-4C to the option bus. (The panel can support up to 4 FPP-RANC-8A-4C 's on the option bus).
2.) Use either NAC 1 or NAC 2 of the FACP to the input 1 of the FPP-RNAC-8A-4C out of input on to the AV's on the loop. Set Bank 1 Dipswitches (S1) all Off - (Follower). Bank 2 Dipswitches (S2) set Dipswitch 0 to On, Dipswitches 1 and 2 set the AC fail Delay. Set Dipswitches 3, 4, 5, and 6 to Off.
*Note: In this cinfiguration the Trouble contact of the FPP-RNAC-8A-4C need to be monitored by the FACP.