Welcome to the forum, @Chinx! When you get a chance, please introduce yourself here. I'd also encourage you to add a real picture as your avatar because it helps build community!
The error message about the port 38156 suggests that you are doing something unusual because no where in the instructions at https://docs.opendatakit.org/aggregate-do/ do we use that port. Did you deviate from the instructions? If so, how?