I'm assuming the client has specific number of connection attempts and then goes quiet. It will most likely show up in your logs again after the next power disruption.
I had a bit of a problem yesterday after a couple of weeks of no issues. I opened the Asus router iOS app on my phone and was told that the router was not connected to the internet. I opened the router GUI from a PC and saw that the router was disconnected. But, all the WIFI and LAN clients could still connected to internet sites!
I tried to reboot the router from the GUI. No soap.
I tried to change the DNS resolvers. No soap.
I ave two AX86U Pro's. One a year newer than the other. The older was being used as the router while the newer as the AiMesh node. Thinking hardware failure of the older router I powered down the node and hard factory reset it to set up as the router successfully. I then hard factory reset the older device and set it up as the AiMesh node successfully.
As it was late in the day and I knew I would get flack for the network being down I did not save the log file. I suspect that the router could have been hit by malware but have no proof. Yes, I do have port forwarding open to a web server but I have no indication that was compromised.
The network is running fine now and still on the beta firmware.