Can't start multiple instances since moving to OTP

I have two instances up and running on the same server since a while now (maybe 2 or 3 years idk) with no problem. But since I updated from source to OTP releases, only one instance can start at a time, the other will only print :

Protocol 'inet_tcp': the name pleroma@127.0.0.1 seems to be in use by another Erlang node

I've been pointed to do elixir --name pleroma@127.0.0.1 -S mix phx.server and replace pleroma@127.0.0.1 by somename@127.0.0.1 but since I'm on OTP I don't have access to mix phx.server.