We're a small org with a github connected to heroku. All of our repos were cloned between April 8 and April 15 with the majority of them having no activity for several years. The audit logs don't show this, you can only see this information in the traffic graphs (/graphs/traffic). If you're seeing cloning of repos that you haven't touched in a while, you've likely been compromised.
For anyone not on a pro plan: I believe you can upgrade and still see the past two weeks of data. I cloned a few of my private repos last night to see how that affects my security logs and no logs appeared. I later upgraded to pro and visited /<username>/<repo>/graphs/traffic and can see the clone counts from before I upgraded. I also can see visitor counts from about a week ago. These clones still don't appear in the security logs though.
I tried upgrading my org to a Team to check traffic, but the upgrade seemingly did nothing. I do have sponsorships, so maybe it’s waiting until my next billing cycle? Can’t figure it out.
Are you on an enterprise plan or a personal one? I know personal plans have limited logs, but I'd hope the enterprise ones would show clones (in reality, they both probably should). Kind of defeats the purpose of an audit log if it doesn't.