Not sure how you prefer to get bug reports, feel free to point me to the right place if there is one.
It looks like there's a bug in the update migration tool on Linux. Migrating was working fine on b4022, b4023 is erroring out with the following:
root@235239af3cbd:/opt/CumulusMX# dotnet MigrateData3to4.dll
Unhandled exception. System.IO.FileLoadException: Could not load file or assembly 'MigrateData3to4, Version=1.0.0.8, Culture=neutral, PublicKeyToken=null'.
Aborted (core dumped)
This is being run on a consistent OS build that's being destroyed and recreated between test runs so I think it's unlikely to be an OS issue.
Let me know if there's any further info I can provide.