On Linux, since v3.11, it seems that Lattice Diamond can only detect a FTDI cable if the kernel driver ftdio_sio has been removed.
On v3.10 and before, it was possible to just unbind the ftdi tty (ttyUSB*) with a udev rule (many blogs which explain how to install Diamond on Ubuntu mention such procedure - example) and not to have to remove the ftdio_sio driver.
Does anyone know a way to still run the Lattice programmer without having to remove the ftdio_sio driver since v3.11?