Stress tests
Sometimes the weirdest shit is more stressful than "yank the power"
I have a Linksys WRT1200ACv2. It has no problem with "yank the power"
Pull out the WAN cable, however, and it loses its shit. It changes its IP to a random 192.168.x.x or 10.0.x.x subnet, loses all the DHCP reservations, and loses all the opened ports in the firewall. The only way to find it on the net is to do a DCHP request and find who answers.
Very annoying and I only discovered this long past the time I could return it to Best Buy. Installing openWRT fixed it though.