Ah you mean a “code project”. A source build is when you build the entire editor from source with a modified engine.
It can still do all of the normal tasks on the Mac that it’d do on the PC even if it’s just blueprint-only, but it will also sign it correctly with an App Store provisioning profile which is what the game needs to be sold. That’s the part other than compilation that Windows can’t do. (This is for people following in my footsteps after this wondering why we’re bothering.)
I’ll have a go at pinging it, but the IP is definitely correct and everything’s set up for SSH. There could be some router funkiness going on, it is the main common element here.