Steps to reproduce

1. With a brand new system, e.g. C6920 that has never had TwinCAT installed, run the silent install
   TC31-XAR-Setup.3.1.4024.55.exe /s /clone_wait /v"/qr REBOOT=ReallySuppress ALLUSERS=1"
2. Using C:\TwinCAT\3.1\System\TcRteInstall.exe, install real time drivers on an appropriate network interface
3. Note that the drivers show as installed when selecting "Show bindings", under "Compatible devices", however the devices do not move to the "Installed and ready to use" category
4. If you try to open TwinCAT and scan devices, it does not work, and adapters don't show up under "Search..." in the EtherCAT master adapter tab

Now, install TwinCAT XAR using the graphical installer. You can select the "Repair" option. After repairing, the adapters now work and driver can be installed properly.

Now, uninstall XAR again, and use silent install. This time it works.

It seems like the silent install does not install everything necessary for the system to function.