This is an uncommon problem, but sometimes it does show up, so it's worth my explaining why it happens. The board uses a standard http protocol for connections between it and you, the reader. Some other sites (such as FossilFly) use a secure https protocol instead. It's their choice. But by doing so, sometimes the site using the https protocol for connections makes all links from it ask for the secure protocol as well - so if, e.g. FossilFly links to the GMB the link will try and use the https secure protocol. And that's when the untrusted connection message appears.
There is no issue with the GMB being untrusted, as it does not need to use an https (i.e. that's what being trusted means). If you are on a site which is using an https and then navigate via a link to the GMB or any site using plain http, you will get a warning if your browser is set up to tell you that you are leaving a trusted server (https) for an untrusted one (http).