Hello,
I have encountered the exact same problem, but what’s peculiar is that when I set the SiteURL to use “http” (without “s”), everything works perfectly fine. However, if I configure it to use “https,” it breaks, and I receive this error. Apart from this issue, everything else appears to be functioning normally, and I’m quite fond of the software. Do you have any ideas about what might be causing this?
By the way, I also have an Nginx reverse proxy in front of the Mattermost server, which is running on a Kubernetes cluster using the Helm chart (Teams edition).
Greetings from Germany!