It's not Unity analytics per-se. I'm calling a PHP script on my own server.
I really appreciate your help, by the way, but I'm happy to slowly debug this on my own. If I work out what's up with it I'll post here to let others know.
Viewing post in Unity WebGL and CORS
Hey! Not sure if you still have this issue, I found this thread by looking for a solution myself.
I fixed the "mixed active content" error by switching to UnityWebRequest instead off the WWW class I was using. Seems the WWW thing defaulted to http regardless of what you wrote in the URL. At the same time I forced my server to only accept https, I did these at the same time so I'm not sure if the force https thing is needed. Hope it makes sense :)
(And check out my thing here if you want ;-) https://aergia.itch.io/the-city-haze )