I did what you say and still had the same issue, I turn it off for one day after that it work fine for two hours then it came back.
This is the log after i turn it on today
log-1691395464123.txt
The modem is D-link DIR-853/ET, and I didn't have any issues with the modem also I tried to unplug the router from the power, and still had the same issue.
The R2 in the modem DMZ.
losing internet connection consistently and it just reconnects every 30 seconds then disconnect again, and I can't access the home page.
log-1690955178382.txt