JBrowse Error: HTTP 200 when trying to view tracks

I am trying to follow this tutorial here: https://galaxyproject.github.io/training-material/topics/visualisation/tutorials/jbrowse/tutorial.html

I am using a local installation of Galaxy v.19.01 and JBrowse 1.16.5+galaxy5. I whitelisted JBrowse and imported the datasets via the links from the tutorial to my history.

JBrows itself seems to run fine, but when I want to look at the results, as soon as I open a track I get the following error messages:

An error was encountered when displaying this track.
Error: HTTP 200 when fetching http://XXXgalaxy/datasets/f0e0bb0fb5(...)/display/data/raw/6aa7a84(...)_0.gff.gz bytes 0-262143

I’d be happy for any tips why this happens and how to solve this.

thanks,