Thanks! That's exactly what I was looking to confirm. And thanks for the tip on HSTS, I'll look into that!

I mean the automatic referrer data that gets us information like what website someone was referred from/clicked from which in GA would show up under the acquisition referrals report. We are not using UTM parameters to designate this traffic. In this case I think the server and browser should be able to communicate that data without dropping it because of the redirect (I know it would get dropped if we were actually going from https to http, but because of the redirect we are going from https to https), but that's not what's happening. The data gets dropped unless we change the link (which redirects to https) from http to https. It's an easy fix obviously, but I'm interested to know why this is happening so we can advise clients on how these issues can be avoided in the future.

I am trying to resolve a referral data issue. Our client noticed that their referrals from one of their sites to another had dropped to almost nothing from being their top referrer. The referring site SiteA which is an HTTPs site, held a link to SiteB, which is also an HTTPs site, so there should be no loss, however the link to SiteB on SiteA had the HTTP protocol. When we changed the link to the HTTPs protocol, the referrals started flowing in.

Is this typical? If the 301 redirect is properly in place for SiteB, why would we lose the referral data?