Don't use Assembly2. It is obsolete.
Use A2plus Workbench, which is based on the former but not compatible.
The server was down. This has been already solved.mlampert wrote: ↑Sun Dec 08, 2019 6:36 pm...
Edit: just saw that there is a wider discussion going on: https://forum.freecadweb.org/viewtopic.php?f=8&t=41531
You want the resulting copy to have the same dimensions, lengths, as the original? Just use the Sketcher_ConstrainEqual on the mirrored elements.