In your access log, you may sometimes see multiple entries from one IP address, possibly requesting your login page.
Almost every time you see subsequent requests from one IP address that seem to be mechanical, you're seeing a search engine crawl your site. At times, search engine crawlers get confused and crawl some pages multiple times. Check the "user agent" of a particular access by clicking on it in your access log to check if the client is reporting itself as a bot.
If someone is actually trying to log into your site and fails, Squarespace will display a (Login Failed) message next to that particular hit.