Great analysis, I agree. The purpose of the hotkey was to provide a nudge that players can use to micro the build range of the engineers. That way you don't need to do a move order before each build order. You just have to time hotkey at the right moment. There are more, alternative and unforeseen side effects to this hotkey. Some are mentioned by @Nomander . There's been earlier discussions to just remove it. And I think I'm in favor of that because of these side effects. I'm not sure about integrating it to automate it - that was not the purpose, and it changes the game in a similar way that area commands do too in my opinion. Which some players were very negative about.

IssueMove(tableOfUnits, position) https://github.com/FAForever/fa/blob/deploy/fafdevelop/engine/Sim.lua#L870 Have in mind those command only work in the SIM-State of the game. That means all players need this mod installed in a network game or you will get desyncs. Before you ask, there is no move command for the UI-State of the game.

The Game.prefs File was the problem. After deleting it everything worked fine. Thanks @Amygdala for the help