Hello Rasmus Teuchler,
Thank you for the details of the issue you are experiencing with the Logic Remote. I found a few resources that I think might help.
First, I recommend checking to see if Garageband is the application controlled on the Logic Remote app:
If you are still not able to connect with Garageband, I recommend the following articles for additional troubleshooting steps (these articles refer to Logic Pro X, but the steps are relevant for Garageband as well):
Thank you for using Apple Support Communities.