Thanks for this detailed information!
There are two problems here. We have fix for the problem with poor information about the status of the fork here: feat: handle non blocking errors on fork by lorenzo-cavazzi · Pull Request #1351 · SwissDataScienceCenter/renku-ui · GitHub
We expect it to be available on RenkuLab soon (we are currently planning an update the week of June 21).
The second problem, that the image is not built, is not yet fixed, but there is a workaround.
Building an image – on error
If the docker image build failed, then you will be given the option to rebuild in the UI:
Building an image – on not available
When there is a problem with forking, though, what typically happens is there was never even an attempt to build the image.
In this case, the easiest way to fix the problem is to push a commit to the repository. One way to do this is to launch an environment using the base image, then modify some file (for example the README), commit and push that.
If you do that, then the pipeline to build the image will be triggered.
Sorry that this is a bit complicated. We will work on making it easier to recover from this error. The instructions above a quite compressed. Let us know if you have any questions, and will fill in any details you need.