I just up upgraded to Mattermost 3.0.1, and everything is running apart from two things:
Mattermost doesn’t pick up the old profile pictures (even though the folders are there). Reuploading them fixes this.
When I try to save settings in the system console I just get the error We received an unexpected status code from the server. (500). The config.json file (like everything else in the mattermost folder) is owned by mattermost:mattermost. So I don’t think it’s a file permission problem.
I’m having the same issue saving changes in the system console.
I fixed the profile picture issue by chown-ing the mattermost folder with the user account I run it under. Profile pics were still there but was getting access denied on the file in the browser. I am still missing some webhook profile pics though, but other shown up. I get a 404 on static/images/webhook_icon.jpg
For your profile images, you might want to check what value you have for FileSettings.Directory in your config.json, and the permissions on that folder.