Hi...What are your settings in the CyberPower PowerPanel?I'd suggest performing some more testing too, pull the power from the wall and do a rundown test with different loads (router only, router + PC + monitor, PC + monitor). Do they all exhibit the same results that you're reporting here?
I've seen more UPSes stay on in the event of a low load with no wall power rather than turn off, unless they were configured to do so or had a circuitry or battery cell issue. Those usually exhibit different symptoms as well. I suggest starting with verifying how PowerPanel is configured and load testing via software and manually.