Browsers frequently fail to connect

My wife's iMac running Big Sur frequently fails to open an URL from a link in multiple websites.

She is getting "An error occurred during a connection to...[URL]. Try again in a few seconds."

The failed URL is not in the link clicked, so I think it is being highjacked, or something. i.e., readersdigest.com has link(s) that, "fails to connect to p.liadm.com."

If I inspect the Readers Digest page and search for p.liadm.com, it is not found.

I have reinstalled Big Sur, used Terminal to flush all caches, tried with and without piaVPN, made sure the browsers (Brave and Firefox) are allowed thru the Firewall. Rebooted the router, even though my iMac is on the same router and it doesn't get the connection error...unless it's so seldom I don't remember.

Removed and reinstalled browsers. Installed Malwarebytes which found nothing.

We have a very stable Gb fiber-optic connection.

Save me, guys! If I don't get this fixed soon my wife will jump out of her wheelchair and strangle me!

Thanks for your help!

Al