There isn't just a red button: there's also a text below it, explaining why the button is red.
or is it a bug that Simbrief is not loaded automatically when GSX starts
A very welcome change from the previous version is that now, the Simbrief connection is made in multi-threading, so the menu opens faster, because Simbrief data is read in the background, while before the menu didn't open until the Simbrief connection was tried (either successfully or not, it would still take a bit of time), which means the button status is not already updated when you open the menu, but it will be as soon the Simbrief data finally comes so, depending on your connection, it will take a variable amount of time, but the menu will update when you open it again, it's not really required to click the Reload button again, even if it will work if you do it anyway.