There is a known spam click bot problem where spam filters check every link in the email. Do some research here on issues.
Is this a tracking error with Marketo or Google Analytics?
It's not a Marketo issue at all if you're talking about GA hits.
And I wouldn't be convinced it's a tracking "error" with GA so much as as underlying error with your links. For example, if you have a link anywhere in the email that redirects to your fallback page and an anti-phishing mail scanner visits that link, you will see a hit in GA.