I am also coming across this issue, I have a RAX120 NetGear router and both the logs and the notification show the alarm regarding attempted access to a block website, however, the domain specified is not included in any policies or rules. See message recorded in the logs below:
[email sent to: email_account Thursday, October 14, 2021 14:06:49
[site blocked: au.download.windowsupdate.com] from source 10.0.0.12, Thursday, October 14, 2021 14:06:41