I don't know why that would be, assuming you've cleared your cache and everything. I haven't used Unity analytics. What happens if you change it to a completely different https URL? Do you get the new URL, but with http instead of https? Do you still get the old URL? Or does it actually work and you get the new URL with https?
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 )