150 signups in 24hrs, no way to know the source [help]

In the past 24 hours, my startup website received 721 unique visitors for 150+ signups (and counting). It's way more than usual.

In Beam Analytics, everything goes into "Direct" traffic. In Google Analytics, it goes into "Unassigned".

Kind of a mess. I have no way of knowing where it comes from. It has obviously been shared by someone with an audience, but can't find where.

Do you know of any hack to get the information?