Comment 1 for bug 1922811

Thank you for taking the time to report this bug and helping to make Ubuntu better. Please execute the following command only once, as it will automatically gather debugging information, in a terminal:

apport-collect 1922811

When reporting bugs in the future please use apport by using 'ubuntu-bug' and the name of the package affected. You can learn more about this functionality at https://wiki.ubuntu.com/ReportingBugs.

FYI: Ubiquity is a little fragile if you use back on some of the later pages (esp. after partition layout has been started), however your description reads like you selected BACK before that, however without the apport detail being uploaded, this bug will be hard to fix. A replacement installer is under construction.