[BUG] Cannot auto migrate to SAMM 2.1.0

[chris-volk]

How: List of performed steps

• import package
• initiate the migration, choose auto-increase namespace version

What: Actual result vs expected result

• Should migrate all models to SAMM 2.1.0 (and auto-increase model version if chosen), but instead fails (long wait, then a failure message).
• Should be able to afterwards load and edit the models, but currently greyed out
• If instead, auto-increase namesapce version is not chosen, the migration is successful, but the models cannot be used.
• If afterwards choosing to migrate the models, a similar problem appears.
• 

As a consequence, the non-migrated models cannot be used.

Where: (e.g. component, version, url, your system info) 5.3.0, but also earlier versions (e.g. 5.1.0?)

Additional context (e.g. references)