When I list all running processes under my username (using "ps -u [username]"), I don't have anything related to Python or Lumerical, even after the force quitting, but still the call to lumapi.FDTD() hangs when I try again (to be more precise, there is another user running Lumerical on the same server, so there are some Lumerical processes on the system, but they should be unrelated to my problem I think ?)

That's why I am a bit puzzled by this problem : I don't see anything on my system persisting between Python sessions (or in general between uses of the API, as I can see the same problem when using the API with a C programm), but still there is something somewhere stuck that prevents me from using the API unless I reboot the server ...