Every system connected to the internet presenting services to the outside world will be automatically hit by scanners, misfits etc. all the time. Normally they'll be scanning for easier to abuse targets, but there are definitely those hunting for Anyconnect servers out there.
Understandable as Anyconnect has had a few security issues. Compared to other services, the risk is not that high as Cisco is often very quick in patching those issues. But hey, there's nothing that comes risk-free. 😉