I tried to grab the hotfix by running:
open /Applications/Unreal\ Engine.app --args "-LauncherLabel=QFE3 -AppLabel=Production-HotfixPreview"
from my terminal. It downloaded what I take to be the hotfix (~ 100mb in size I think), and started the launcher. The launcher then started as expected, but in the left hand side where I usually have a ‘Launch’ button, it simply says ‘Please Wait…’. I’ve left it this way for some time (>30m), but there hasn’t been any change that I’ve seen. I’ve also quit the launcher and retried running the terminal command, with similar results.
If I run the launcher without the additional command line information, it works as expected.