LXBeams on iPad v1.2.0 added a major improvement, allowing more than one object to be selected at a time.
However, this also introduced a bug where the app will crash when saving a file with an object selected and with the generate preview preference enabled.
A fix has been submitted to Apple for approval and should be available in the AppStore later this week.
In the meantime, it is recommended to disable the "Generate Preview" preference for v1.2.0.
Thanks to John Velez for providing crash reports that helped isolate this issue.