Yes it is another one of my grievances about this router as it fudges up the syslogs, it has no RTC so every reboot it goes back in time to May 5 , they could have added a script to look at the date stamp the syslog file and update the time from that or left a date in the nvram so it could...
This is actually one of many issues in the Firmware that date back to 2018 , if you do a search you will find that people have been having this problem for years and there are mentions in forums going back to 2018 , Asus is just terrible at releasing new firmware to resolve the problem they have...