I have Alfred 3.7.1 running on two different MacBook Pros -- both running 10.14.2 (Mojave). I have the latest Alfred Remote app on my iPhone which is running iOS 12.1.2.
I can successfully add the iOS Remote to one Mac, but then when I try to add it to the second Mac using the "Add" link in top right of the connection screen on the Alfred Remote app, it will never connect. If I chose the "Direct" connection option from the "Looking for Alfred" screen, then the connection seems successful, but I still only see one of my Macs listed on the "Alfred Remote" screen.
The IP a