Version 1.0.2+dfsg-4 of mu-editor is marked for autoremoval from testing on Sat 04 Jan 2020. It depends (transitively) on python-qtconsole, affected by #938116. You should try to prevent the removal by fixing these RC bugs.
A new upstream version is available: 1.1.0-alpha.2high
A new upstream version 1.1.0-alpha.2 is available, you should consider packaging it.