Jjewel is in the early stages of development so you may run into problems using Jjewel. This page lists common problems and how to work around them.
You may run into this issue if you quit Jjewel and relaunch it. The symptom of the issue is an empty window with the title Repo.
The workaround is to close the window and reopen the repository by pressing Cmd-O.
If you get an error when pushing, make sure you set a bookmark and remote.
Also, make sure the changes you want to push have descriptions (commit messages). Jujutsu won't push changes that don't have a description.
If you find an issue with Jjewel, choose Help > Report a Bug to send an email about the issue to get it fixed.