Preparing Library dialog never went away. After several minutes, took samples and forced quit. Logos opened normally upon restart.
Sample from Activity Monitor
3323.Sample of Logos.txt
Sample from Logos Logging Utility
4617.LogosLogs.jackcav.20190829-053922.zip
Apple Crash Report
1464.Apple Crash.rtf
Oops—Neglected to archive Logos Logs before restart [:$]