If it is the BOOSS amp I think it is, it’s RMS output at 14.4v is around 350 watts, max. (30A Fuse x 14.4 volts x.80) provided it is actually running at 80% efficiency. Assuming the RV 600.1 is running at the same efficiency, they are both putting out around 300-350 watts of power.
Now, to isolate the issue, first, check the amplifier fuse. Then, mark the BOSS amps RCA’s with a piece of tape. Remove them and the ones in the Rockville amp. Since we know that the signal is getting to the BOSS and that the amp is working and that sub is getting sound, nothing to see there. Plug the RCA’s from the BOSS amp into the Rockville, test it. If good sound, you have a BAD set of (or single) RCA(s) going to the Rockville. If no sound, you may have a bad amp. Now, plug the RCA’s tape marked RCA’s back into the BOSS amp. Now, disconnect the speaker lead from the sub that yu know works and run them to the other sub, just to confirm that the sub that isn't working is not the issues. This should isolate the issue to the RCA’s the AMP or the Sub.