I have the exact same problem - I was tracking my visits and page views for the month of April, and it was my highest traffic month of all time... until suddenly I looked at it last week and the numbers were like HALF of what they previously showed. I contacted squarespace support to report it. Had a heck of a time getting them to understand my issue, because they seemed convinced I was just tech illiterate and didn't know what I was looking at. They sent the data they can see for my site, and it's the higher numbers, so the problem is with my analytics panel. The data is still there. I just don't have access to it. Sounds like your situation is the exact same, and that it happened right around the same time, so please do report it, and ask to see their traffic data for the time period in question.
